There have been fresh protests in western China's Xinjiang region, where almost 200 people were killed in ethnic violence in July.
A witness told the BBC that as many as 2,000 ethnic Han Chinese have been demonstrating in the capital Urumqi.
The protesters are said to be angry at the deteriorating security situation in the wake of the July riots.
A trigger for the protests appears to have been a spate of unexplained stabbings using hypodermic needles.
State-run news agency Xinhua said that 15 people had been arrested over the stabbings, and that four of them had been prosecuted and would receive their judgements soon.
A businessman in Urumqi told the BBC that members of the Han community were demonstrating to complain about the worsening security situation.
"Han Chinese people have been protesting in the streets since yesterday," he said.
"Nearly everyone in Urumqi is on strike or protesting. Right now in front of me there are at least 2,000 people," he said from the centre of Urumqi.