Long convoys of armored cars and green troop trucks with riot police rumbled through Urumqi, a city of 2.3 million people. Other security forces carrying automatic rifles with bayonets formed cordons to defend Muslim neighborhoods from marauding groups of vigilantes with sticks.
Military helicopters buzzed over Xinjiang's regional capital, dropping pamphlets urging people to stay in their homes and stop fighting. Special police from other provinces were called in to patrol the city.
The crisis was so severe that President Hu Jintao cut short a trip to Italy, where he was to participate in a Group of Eight summit. It was an embarrassing move for a leader who wants to show that China has a harmonious society as it prepares to celebrate the 60th anniversary of Communist rule.
The heightened security came amid the worst spasm of ethnic violence in decades in Xinjiang -- a sprawling, oil-rich territory that borders Pakistan, Afghanistan and other Central Asian countries. The region is home to the Uighur ethnic minority, who rioted Sunday and attacked the Han Chinese -- the nation's biggest ethnic group -- after holding a protest that was ended by police.
Officials have said 156 people were killed as the Turkic-speaking Uighurs ran amok in the city, beating and stabbing the Han Chinese. The Uighurs allege that trigger-happy security forces gunned down many of the protesters, and officials have yet to give an ethnic breakdown of those killed.
In Rome, a Germany-based Uighur leader, Erkin Alptekin, told The Associated Press that "our countrymen in China" reported that 600-800 Uighurs were killed in the past few days and 3,000 were arrested.
"We were told (by fellow Uighurs) that 140 were dead on the spot" on Sunday and that their bodies were tossed into trucks and taken away by Chinese security forces, said Alptekin, who briefed the human rights commission in the Italian parliament.
"When the Uighurs heard the people were fired upon, parents all came out looking for their sons and daughters," he said, adding that security forces started to "disperse them by force, then started to beat them, tear gas them and shoot them."
His account could not be independently confirmed.
More than 1,100 people were wounded in the violence. Dr. Yuan Hong of Urumqi People's Hospital said most of the people treated at his facility were clubbed, while others had been cut by knives.
Li Zhi, the highest-ranking Communist Party official in Urumqi, told reporters that some of the rioters were university students who were misled and didn't understand what they were doing. They would be treated leniently, he said, as long as they weren't involved in serious acts of violence and vandalism.
But Li added: "To those who committed crimes with cruel means, we will execute them."
He also repeated allegations that the riot was whipped up by U.S.-exiled Uighur activist Rebiya Kadeer and her overseas supporters. "They're afraid to see our economic prosperity. They're afraid to see our ethnic unity and the people living a stable, prosperous life," he said.
Kadeer has denied masterminding the violence, and many Uighurs laughed off the notion that they were puppets of groups abroad.
"Not even a 3-year-old would believe that Rebiya stirred this up. It's ridiculous," said a shopkeeper who only identified himself as Ahmet. Like other Uighurs, he declined to give his full name because he feared the police would detain him.
Ahmet was quick to rattle off a long list of grievances commonly mentioned by Uighurs. He accused the Han Chinese of discrimination and alleged that government policies were forcing them to abandon their culture, language and Islamic faith.
"After all this rioting, I'm still filled with hatred. I'm not afraid of the Han Chinese," Ahmet said.
His neighborhood in southern Urumqi was targeted by mobs of Han Chinese who roamed the capital Tuesday seeking revenge. Ahmet's friends had video shot by mobile phones and cameras that showed the stick-wielding Han men beating Uighurs. He pointed to blood stains on a white concrete apartment wall, where he said a Uighur was severely stabbed.
A Uighur college student who called herself Parizat added, "The men were carrying a Chinese flag. I never thought something like this would happen. We're all Chinese citizens."
The Uighurs accused paramilitary police of allowing the Han Chinese to attack their neighbors. But in the video, the troops appeared to be trying to block or restrain the mobs.
On Wednesday, the government warned residents against carrying weapons on the street, and most people generally complied. But there were groups of Han Chinese who tried to find soft spots in police cordons and rush into Uighur neighborhoods.
One such failed attempt sent a wave of terror and panic through the biggest Uighur neighborhood, Er Dao Qiao.
When someone yelled, "The Han are coming!" children scampered indoors and women ran shrieking through a backstreet market with carts of watermelons, shops selling cold soft drinks and smoky grills with sizzling lamb kebabs.
Within seconds, the men armed themselves with spears stashed behind doors and under market stands. The weapons were long poles with knives and meat cleavers tied to the ends. Piles of rocks were placed across the street for ammunition.
One Uighur graduate student who called himself Memet greeted a foreign reporter in English by saying, "Welcome to the jungle!"
"I think the Uighur people lately are kind of happy. You can see it in their eyes, a bit of happiness. We've spoken up. People know we exist now," he said.
The ethnic hatred in Xinjiang appears to run so deep that many Uighurs won't express sorrow for the Han Chinese who were attacked Sunday.
One of them was Dong Yuanyuan, 24, a newlywed who said she was on a bus with her husband getting ready to leave on their honeymoon. She said Uighur attackers dragged them off the bus and beat them until they were unconscious. Her husband was still missing, said the woman, who had abrasions on her face, arms and knees.
"My aunts have been going to all the hospitals to search for him. He must still be unconscious," she told reporters who joined a government tour at the People's Hospital.
Abdul Rehim, a Uighur with his left arm in a sling, said he was walking with his brother when a group of Han Chinese "just came out and did this to me."
Another victim was Ma Weihong, who said she was walking home from a park with her 10-year-old son when the riot started. The boy suffered minor injuries, but the mother had a broken arm and wrist, missing teeth and head wounds.
"The stores all closed up and we tried to run for home," she said. "That is when they caught us. We couldn't get away."