Outnumbered riot police used tear gas to try to disperse thousands of angry protesters who flooded the capital of the north-western region of Xinjiang.
In a sign of government anxiety about the unrest the city's Communist Party boss Li Zhi took to the streets to plead with them to return home, and overnight "traffic restrictions" - originally announced as a curfew - came into effect to halt the violence, in which many people were injured.
Security forces intervened to stop casualties, breaking up a battle between hundreds of rock-throwing Han and Uighurs and forcing a Han mob to leave a building they stormed in a Uighur area, a Reuters reporter said. There were no reports of deaths.
But riot police stood warily by as crowds vented their anger by throwing rocks at a mosque, and smashing shops and restaurants owned by Uighurs, a Turkic people who are largely Islamic and share linguistic and cultural bonds with Central Asia.
"They attacked us. Now it's our turn to attack them," a Han man in the crowd told Reuters. He refused to give his name.
The crowd had armed themselves with an improvised arsenal of meat cleavers, metal rods and spades seized from building sites, rocks and wooden clubs, and the most extreme shouted "kill them" and "exterminate the Uighurs".
Rioters said they wanted revenge for violence on Sunday. Beijing has not given a breakdown of the ethnicity of the dead, but official media reports initially focused on Han victims and Urumqi's Han community seem sure they were the main targets in the country's worst unrest for years.
Xinjiang has long been a hotbed of ethnic tensions, fostered by a yawning economic gap between Uighurs and Han Chinese, government controls on religion and culture and an influx of Han Chinese migrants who now are the majority in most key cities.
Beijing has poured cash into exploiting Xinjiang's energy deposits and consolidating its hold on a strategically vital frontierland that borders Pakistan, Afghanistan and Central Asia.
But Uighurs, who launched a series of attacks to coincide with the build-up to last year's Beijing Olympics, say migrant Han are the main beneficiaries.
The violence has showed signs of spreading across the volatile region, but its remoteness and poverty meant the trouble had little impact on China's financial markets. Stocks slipped on technical factors while the yuan was trading higher against the dollar.
Uighurs had emptied out of the streets of Urumqi late on Tuesday, as the number and violence of Han protesters grew.
But earlier in the day hundreds came out to demonstrate against the government crackdown in the wake of Sunday's riots, which they say involved an indiscriminate sweep of Uighur areas.
Many were women, wailing and waving the identity cards of husbands, brothers or sons they say were arbitrarily seized.
"My husband was taken away yesterday by police. They didn't say why. They just took him away," a woman who identified herself as Maliya told Reuters. They vowed to keep up their defiance.
Abdul Ali, a Uighur man in his 20s who had taken off his shirt, held up his clenched fist. "They've been arresting us for no reason, and it's time for us to fight back," he said.
Ali said three of his brothers and a sister were among 1,434 suspects taken into custody. Of the 156 killed, 27 were women.
Human rights groups have warned that a harsh crackdown on Uighurs in the wake of Sunday's violence could merely exacerbate the grievances that fuelled the bloodshed.
Almost half of Xinjiang's 20 million people are Uighurs, while the population of Urumqi, which lies around 3,300 km (2,000 miles) west of Beijing, is mostly Han.
Navi Pillay, the UN High Commissioner for Human Rights, said demonstrators had the right to protest peacefully and that those arrested should be treated in line with international law.
"I urge Uighur and Han civic leaders, and the Chinese authorities at all levels, to exercise great restraint so as not to spark further violence and loss of life," Pillay said in a statement. "This is a major tragedy."
Urumqi Communist Party boss Li Zhi defended the crackdown.
"It should be said that they were all violent elements who wielded clubs and smashed, looted, burned and even murdered at the scene," he told a news conference.
Despite heightened security, and a cut to internet services in Urumqi which was confirmed on Tuesday by Communist party boss Li, some unrest appeared to be spreading in the volatile region.
Police dispersed around 200 people at the Id Kah mosque in Kashgar in southern Xinjiang on Monday evening, Xinhua said. The report did not say if police used force but said checkpoints had been set up at crossroads between Kashgar airport and downtown.
Chinese officials have already blamed the unrest on separatist groups abroad it says are seeking an independent homeland, led by U.S.-based exiled businesswoman Rebiya Kadeer.
China's embassy in the Netherlands was attacked by exiled pro-Uighur activists who threw rocks that smashed windows, and two unidentified men threw Molotov cocktails at a Munich consulate a Foreign Ministry spokesman said on Tuesday.
But exiled groups reject the charge of planning the violence and say it was a spontaneous explosion of pent-up frustration.
Wu'er Kaixi, a Uighur and one of the best known dissidents from the Tiananmen Square crackdown in Beijing 20 years ago, said there had been no improvement in China's human rights record.
"For a long time, Uighurs have been discriminated against and suppressed in China," he told a news conference in Taiwan. "So much so that we're almost colonised by China."
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