Internet social platforms and chat programs appeared to have unified Uighurs in anger over the way Chinese officials had handled the earlier brawl, which took place in late June thousands of miles away in Shaoguan, Guangdong Province. There, Han workers rampaged through a Uighur dormitory, killing at least two Uighurs and injuring many others, according to the state news agency, Xinhua. Police officers later arrested a resentful former factory worker who had ignited the fight by spreading a rumor that six Uighur men had raped two Han women at the site, Xinhua reported.

Image Chinese soldiers patrolling the streets of Urumqi Monday. Credit... David Gray/Agence France-Presse — Getty Images

But photographs that appeared online after the battle showed people standing around a pile of corpses, leading many Uighurs to believe that the government was playing down the number of dead Uighurs. One Uighur student said the photographs began showing up on many Web sites about one week ago. Government censors repeatedly tried to delete them, but to no avail, he said.

“Uighurs posted it again and again in order to let more people know the truth, because how painful is it that the government does bald-faced injustice to Uighur people?” said the student, who spoke on the condition of anonymity for fear of retribution from the government.

A call for protests spread on Web sites and QQ, the most popular instant-messaging program in China, despite government efforts to block online discussion of the feud.

By Tuesday morning, more than 36 hours after the start of the protest, the police had detained more than 1,400 suspects, according to Xinhua. More than 200 shops and 14 homes had been destroyed in Urumqi, and 261 motor vehicles, mostly buses, had been burned, Xinhua reported, citing Liu Yaohua, the regional police chief.

Police officers operated checkpoints on roads throughout Xinjiang on Monday. People at major hotels said they had no Internet access. Most people in the city could not use cellphones.