The truck, loaded with margarine and flour, continued into the tunnel towards Italy forthree miles before bursting into flames, causing the worst road tunnel accident in history.
The conflagration - described by one firefighter as "like a crematorium hundreds of metres long" - is now feared to have killed at least 41 people.
For 600 metres behind the Belgian truck, firefighters have counted a queue of 30 twisted and melted vehicles - 20 trucks and 10 cars, often dozens of yards apart - which exploded one by one as the heat in the tunnel rose to more than 1,000 degrees centigrade.
The drivers of the first few trucks, including the driver of the Belgian lorry, ran to the Italian end and escaped without injury. The occupants of the vehicles trapped behind are believed to have been overcome by the fumes and heat from the original fire before their cars and trucks exploded.
Three left their vehicles in attempts to reach safety but collapsed in the roadway. Three died in sealed escape chambers, which had provided sanctuary for only two hours. Onebody was found in the trailer of a truck and may have been a stowaway or illegal immigrant.
"The sights in the tunnel are unimaginable, fantastic, apocalyptic," said one senior fire-fighter at the French tunnel entrance. "There are heavy trucks which have melted into the tunnel floor until they are no higher than a car. Many of the bodies have been incinerated. All that remains are a few blackened bones."
The grim task of removing the bodies continued yesterday but the heat in the tunnel - four days after the catastrophe - is still so high it will be severaldays before all the wrecked vehicles can be removed. The dead are feared to include the British driver, Martin Cairns, 23, whose truck is believed to have been one of those trapped behind the blazing Belgian lorry. Other victims are presumed to include a French family of five and an Italian family of four.
One of those who died in a two-hour sanctuary was Pierlucio Tinazzi, 34, an Italianworking in the tunnel. His remains were found 48 hours after he had made several journeys into the heat and fumes to rescue motorists on the pillion of his motorbike. He was overcome by fumes on his 10th rescue. He had reached a refuge with a motorist but both men were asphyxiated.
An official at the French tunnel mouth yesterday confirmed a news agency report that a tunnel official saw white smoke pouring from the Belgian lorry when it was only two kilometres into the tunnel. The official said the security officer saw the smoking lorry on a television monitor screen but decided it would be better to let the truck continue towards Italy, rather than try to stop it or turn it around in the narrow (seven metres by eight metres) tunnel. A videotape has been handed to detectives investigating the disaster.
By the time the Belgian driver did stop - alerted by trucks coming the other way - his lorry was 6.5 kilometres into the tunnel, just past the half-way mark, and already alight.
If it had stopped earlier, it would have been much easier for fire-fighters to reach the scene; the disaster might have been less serious or avoided altogether.
This is just one of a number of apparent failings in the tunnel security arrangements - emergency telephones not working; fresh air not reaching at least one sealed safety chamber; only one fireman on duty - which have come to light in the past few days.
There are also grave doubts about the tunnel's under- carriageway ventilation system, which is supposed to be able to extract 300 cubic metres of fumes a second. Tunnel officials have admitted the system did not work well at first.
It failed to deal with the thick fumes from the burning margarine and flour in the truck, allowing smoke and heat to build up to a point which made it impossible for the Chamonix fire brigade to get within two kilometres of the blaze. The firemen had, themselves, to be rescued.
One - Georges "Jojo" Tosello, the deputy fire chief - died on the way to hospital. He had not worn breathing apparatus because the six fire- fighters had only four sets among them.
All these issues will be examined by the two investigations being carried out: the first is a government inquiry, which is expected to give its initial report by mid-May; the second is criminal investigation into possible charges of "aggravated manslaughter", which may take two years or more. There is a separate criminal investigation into the death of the fireman.
The mayor of Chamonix, Michel Charlet, the head of the local fire brigade and local environmental groups, have been warning of a possible catastrophe in the tunnel for years.
It was built mostly with cars in mind, they say, but traffic has grown in recent years to more than 4,000 cars and 2,000 trucks a day.
Mr Charlet is calling for heavy good vehicles to bebanned from the tunnel; others in the valley say it should be closed altogether or rebuilt.
The Belgian driver of the truck which began the catastrophe has been absolved of all blame and was allowed to return to Brussels on Saturday night.
Gilbert Degrave, 57, his face swollen with distress and exhaustion, said: "I can't sleep. I wake every ten minutes ... I thought at first that it was just my truck which was destroyed, then I heard on the news that there were 10 dead, now 40. It's just unimaginable."Reuse content