The noise of the explosions was deafening, shaking the ground, shattering windows, setting off car alarms. Bullets and shrapnel flew out in flaming arcs, setting fire to part of a checkpoint and sent families with children scurrying for cover.
The blasts reverberated for 22 minutes, sending the local social network into a frenzy: Mariupol was once again under attack. Car-loads of fighters set off from Donetsk and Slovyansk to provide support. But there was no raid by forces of the Kiev government: an armoured personnel carrier it had abandoned had been set on fire; the massive blasts were the result of ammunition detonating inside.
It was, according to differing accounts, a deliberate decision by separatist militant commanders to destroy the carrier, sabotage by fifth-columnists or – the most likely explanation – the handiwork of drunken pickets who had been manning a freshly erected barricade made from the contents of City Hall, which had been gutted the previous evening.
The febrile atmosphere was, however, understandable. Apart from any attacks, a referendum due to be held today by pro-Russian separatists in a number of cities in eastern Ukraine, including Donetsk, aimed at triggering independence, was also stoking tensions.
Ukraine's acting president, Oleksander Turchynov, declared yesterday that a vote for independence would be "a step into the abyss for these regions". "Those who stand for self-rule don't understand that it would mean the complete destruction of the economy," he said.
Mariupol has been the focus of repeated attacks by government forces. The latest came on Friday, on one of the most revered anniversaries in the Russian-speaking half of the country: the commemoration of victory over Nazi Germany. An assortment took part in the assault, including a private army supposedly bankrolled by an oligarch – the "men in black". It left between seven and 20 people dead, depending on accounts, after fierce clashes centred on the main police headquarters.
The government claimed that its attack on the building, setting it on fire, came only after protesters had occupied it with the aim of taking over the armoury. Residents angrily disputed this, insisting that "fascists" from Kiev had tried to storm the building to get hold of the weapons, shooting at the police, because they knew the local force "would not turn against the people".
In pictures: The Ukraine crisis
In pictures: The Ukraine crisis
1/39 Ukraine crisis
Ukrainian soldiers from the 'Azov' battalion guard their base in Mariupol, Donetsk
2/39 Ukraine crisis
Children were transferred from orphanages in Donetsk and Makeyevka to escape the fighting between the Ukrainian army and pro-Russian separatists
3/39 Ukraine crisis
Ukrainian servicemen captured by pro-Russian separatists sit on the ground as they are assigned to clean a street in Snizhne in the Donetsk region
4/39 Ukraine crisis
A view inside the Youth Culture Centre destroyed by pro-Russian separatists in Donetsk
5/39 Ukraine crisis
A woman holds a portrait of her dead son as she speaks during a rally in front of Ukrainian President Petro Poroshenko's office in Kiev
6/39 Ukraine crisis
A boy ascends the stairs of a bomb shelter after the shelling in the Petrovskiy district in Donetsk
7/39 Ukraine crisis
A medic looks at thirty coffins prepared for the funerals of pro-Russian rebels killed during heavy fighting at Donetsk airport, outside a Donetsk morgue
8/39 Ukraine crisis
Relatives mourn near the coffin of Mark Zverev, a taxi driver shot dead during clashes at the Donetsk airport between Ukrainian troops and the pro-Russian rebels, during his funeral in the village of Grabari on the outskirts of Donetsk
9/39 Ukraine crisis
Medical workers carry a wounded pro-Russian militant on a stretcher after armed clashes occured between pro-Russian gunmen and Ukrainian troops in Slavyansk
10/39 Ukraine crisis
A member of a newly-formed pro-Russian armed group called the Russian Orthodox Army mans a barricade near Donetsk airport
11/39 Ukraine crisis
Black smoke rises from a shot down Ukrainian Army helicopter outside Slovyansk
12/39 Ukraine crisis
A woman is overcome with emotion as she looks at blood stains and damage around a wrecked truck of supporters of the self-proclaimed 'Donetsk People's Republic' on road leading to the Donetsk International Airport
13/39 Ukraine crisis
A local man looks at damage near a wrecked truck of supporters of the self-proclaimed 'Donetsk People's Republic' on road leading to the Donetsk International Airport
14/39 Ukraine crisis
A bloodstained icon of Jesus is seen among blood soaked shattered glass atop a wrecked truck near the Donetsk airport
15/39 Ukraine crisis
A family member attends a funeral for Olga Prokhorenko (60) who was killed by shrapnel after Ukrainian government forces shelled their location, during the funeral in Slovyansk
16/39 Ukraine crisis
A woman reacts after seeing the lifeless body of a man killed by shrapnel following a shelling from Ukrainian government forces in Slovyansk
17/39 Ukraine crisis
Pro-Russian militants take position on the roof of the international airport of the eastern Ukrainian city of Donetsk
18/39 Ukraine crisis
A woman embraces a pro-Russian separatist from the "East" battalion during a rally in the eastern city of Donetsk
19/39 Ukraine crisis
A Ukrainian helicopter Mi-24 gunship fires its cannons against rebels at the main terminal building of Donetsk international airport
20/39 Ukraine crisis
A pro-Russian gunman changes his position near the airport, outside Donetsk
21/39 Ukraine crisis
A pro-Russian gunman aims his weapon near the airport, outside Donetsk. Ukraine's military launched air strikes against separatists who had taken over the airport in the eastern capital of Donetsk in what appeared to be the most visible operation of the Ukrainian troops since they started a crackdown on insurgents
22/39 Ukraine crisis
Pro-Russians ride on a truck in Donetsk. A convoy of an armored personnel carrier and seven trucks carrying several hundred heavily armed men drove through central Donetsk and gunmen got out of the trucks, stood to attention and gave shots in the air in jubilation as a crowd of several thousand supporters cheered them and chanted: "Heroes!"
23/39 Ukraine crisis
An elderly woman leans against the chest of a pro-Russian gunman in Lenin square in Donetsk
24/39 Ukraine crisis
Pro-Russian militants guard a psychiatric hospital after shell explosions during the fighting between pro-Russian militants and the Ukrainian army, in Semyonovka village, outside Slavyansk
25/39 Ukraine crisis
Ukrainian troops stand guard at a checkpoint on the road near the eastern city of Izum, Donetsk
26/39 Ukraine crisis
Members of the Democratic Alliance party take part in a performance in front of the French embassy in Kiev. Protesters set up a pool with the blood of animals and models of warships in a protest against French plans for the sale of two Mistral helicopter carriers to the Russian Navy
27/39 Ukraine crisis
A man carries a portrait of pro-Russian activist Vadim Hudich, who was killed in a shooting incident at the head of a funeral procession in the eastern Ukranian town of Krasnoarmeisk
28/39 Ukraine crisis
A voter is seen inside a voting booth at a polling station during the referendum on the status of Donetsk region in the eastern Ukrainian city of Donetsk
29/39 Ukraine crisis
Members of a local election commission sort ballots as they start counting votes of referendum on the status of Luhansk region in Luhansk
30/39 Ukraine crisis
Members of a local election commission empty a ballot box as they start counting votes of the referendum on the status of Donetsk region in Donetsk
31/39 Ukraine crisis
Members of a local election commission empty ballot boxes as they start counting votes after a referendum, at a polling station in Lugansk
32/39 Ukraine crisis
Local residents watch as others give first aid to a man who was shot in the leg by Ukranian militia in the village of Krasnoarmisk. Eyewitness said that Ukranian militia tried to stop the referendum voters briefly taking the City Hall of Krasnoarmisk, where unarmed pro-Russian supporters were gathering. Reportedly the Ukranian militia came out out the building and started shooting at the people, killing at least one man and leaving at least two others injured
33/39 Ukraine crisis
Members of a local election commission count votes after a referendum organized by the so-called Donetsk People's Republic members at a polling station in Donetsk
34/39 Ukraine crisis
Voters visit a polling station to take part in the referendum on the status of Donetsk
35/39 Ukraine crisis
An Armoured Personnel Carrier (APC) with a Russian flag drives through the center of Slaviansk during the day of referendum organized by the so-called Donetsk People's Republic members in Slavyansk
36/39 Ukraine crisis
A statue of Lenin is placed in front of a pro-Russian barricade on the outskirts of the eastern Ukrainian town of Slavyansk
37/39 Ukraine crisis
A feamle veteran (C) sings during 'Victory Day' celebrations in Donetsk
38/39 Ukraine crisis
People stand near the burning Mariupol police station
39/39 Ukraine crisis
Ukrainian soldiers stand guard beside an armoured personnel carrier at a checkpoint in Mariupol. Ukrainian forces seized the rebel-held city hall in the eastern port city of Mariupol, driving out pro-Russian activists, then withdrew, making no attempt to hold onto the building
It was unclear just how many were killed in the clashes. I saw two bodies, one of a police officer and another a civilian with an armband of Ukrainian colours. This person was part of a group, according to residents, who had appeared in support of the troops. Two others were brought out of the building and, including reports from the hospitals, the number of deaths was likely to be around 10.
The country's excitable acting interior minister, Arsen Avakov, who keeps a fairly unreliable chronicle of military matters, wrote on his Facebook account: "A terrorist group of about 60 men armed with automatic weapons attacked the police headquarters … About 20 terrorists were destroyed and four taken prisoner. To those who come with weapons and who shoot … To them there can be only one answer from the Ukrainian state – annihilation."
Mr Avakov's postings are normally treated with scepticism but this one was seized on by some in Mariupol. "He is right about more being killed than the media is saying," maintained Yuri Koralinkov, a pro-Russian activist. "In fact, the number was 36, most of them in there," he said, pointing to the charred shell of the police headquarters. The front steps had been turned into a shrine of flowers and candles. Turning back from them, Ludmilla Vladislavia corrected: "No, it was 42. I heard it myself from the firemen. This is another Odessa."
Others were quick to take this up. It was a highly emotive comparison: up to 55 people had died there, separatist demonstrators, after being trapped in the city's trade union building by a nationalist crowd, which had then set it on fire with Molotov cocktails.
"This is now the junta's favoured form of murder, burning people to death. They call us terrorists, but it is they who want to terrorise.
"What happened at Odessa disgusted so many people, so many volunteered to join the people's militias. This will have the same effect with the deaths and injuries," Mr Koralinkov said.
At the city's main A&E department, Irina Pomarovna, the deputy director, said around a dozen wounded had been brought in; one of them, a 38-year-old policeman, had subsequently died.
"We got the ones brought in by people in their private cars. Another hospital had got around the same numbers," she said. "There were some burn victims, but also lots of penetrative wounds to chest and abdomen. We were expecting large numbers of casualties because of the rising numbers of attacks; staff dealing with trauma had been on stand-by, but this is still a shock."
There was another type of shock when a woman from City Hall came to collect the personal details of those brought in from the attacks; they had already been given out to two men, claiming to be officials. In Odessa, names and addresses of protesters had been leaked from hospitals and ended up in the hands of Ukrainian nationalists; threats and intimidation had followed.
Andre Petrovich, who had undergone surgery for gunshot wounds to his leg and hip, was not aware of the list that had been inadvertently released. But he was already deeply concerned about his safety. "There have been people arrested in hospital. Not all the police sympathise with the public, some are with Kiev. Also, you have these fascist militias. They, too, can come and snatch you," he said. "So you're vulnerable here."
A 38-year-old-builder had been at the city centre on Friday when shooting began. "I support the idea of an independent Donbas, but I have not really been out on the streets that much," he said. "I saw people shouting at the soldiers and went to have a look. One of them came out from behind a tree and opened fire. I was hit and I fell. Others then dragged me away.
"You have people in Kiev who claim to be a government, but then send tanks [armoured personnel carriers] to attack the citizens of their country. Would you want to be part of such a country? People are voting and they'll vote to leave Ukraine."
Just how easily people would be able to vote in today's referendum on secession was open to doubt, as was the effect the result might have.
Roman Lyagin, the 33-year-old head of the "election commission" of the Donbas People's Republic was confident that "there will be around 20,000 willing to work as election officials, the voter turnout will be around 70 per cent and preliminary results will be announced a few hours after the polls close".
The reality is that the voting list is two years old and no minimum turnout will be required to turn the result into constitutional changes designed to end the state of Ukraine in its present form. There will be no outside observers and no challenges will be permitted.
However, for those who complain about the mounting costs of elections in the West, the People's Republic provides an extremely cheap alternative: just over €1,200 (£980) has been spent, €500 of which went on toners for three borrowed printers for ballot papers.
The question on the paper is: "Do you support the act of self-rule by the People's Republic of Donetsk?" Some residents of the city were puzzled by what that meant. "Is it autonomy or independence? I am against independence but want autonomy in a federal system; this has not been explained," said Eliana Korchinova, a clerical assistant.
Will she vote? "No one has told me where to go to vote. I am not sure they have actually built the polling stations yet."
Germany and France warned Russia yesterday that it would face a further round of sanctions if the Ukraine presidential elections did not go ahead on 25 May.
Chancellor Angela Merkel and French President François Hollande said that the country faced destabilisation if the vote did not occur.
They also called for a visible reduction in Russian forces on the Ukraine border, which Nato has estimated at some 40,000 troops, and warned referendums scheduled to be staged by pro-Russian separatists in eastern Ukraine today were illegal.
The European Union agreed a round of sanctions on 6 March but at a joint press conference Ms Merkel said, "We would be ready to take further sanctions against Russia if the [presidential] elections in Ukraine fail."
Germany, which relies on Russia for 40 per cent of its natural gas, has previously appeared reluctant to broaden sanctions but Ms Merkel now appears more concerned about instability in the region and beyond if the Ukrainian crisis continues.