Thousands of security forces have been deployed in the city of Urumqi in China's Xinjiang region to try to end deadly ethnic clashes.
The show of force comes as Chinese President Hu Jintao cut short a visit to Italy for the G8 summit to deal with the crisis.
The unrest between Muslim Uighurs and Han Chinese began on Sunday and has left 156 people dead. More than 1,400 people have been arrested over the violence.
The BBC reports there are thousands of paramilitary police in the city in a situation which is martial law in all but name. The situation remained tense, with rumours and counter-rumours of ethnic attacks.
Security forces in full body armour and with semi-automatic weapons have drawn a line between the two communities. Fresh scuffles have been reported as police try to arrest protesters.
Reuters news agency said crowds of Han Chinese were volatile and growing. Some were angry that police were arresting young Han men.
Reporters from the AFP news agency also said they had seen fresh violence on Wednesday, including one attack on a Uighur man by Han Chinese. They said the man was beaten and kicked by about six people as dozens of Han Chinese yelled encouragement, before police moved in to end the attack.
President Hu was expected to join G8 talks taking place in Rome on Thursday. Instead he was flying home from an airport in Pisa, leaving officials to represent China at the G8 summit.
A state visit to Portugal has also been cancelled, China's official news agency Xinhua said.
A curfew has been imposed for a second night in Urumqi. Internet access has been cut off in parts of the city.