At least 200 Uighurs faced off against police in Urumqi on Tuesday following news that 1,434 people were arrested in connection with Sunday's riots.
Trouble also spread outside of Urumqi, capital of Xinjiang, with protests on Monday near a mosque in Kashgar.
Beijing blames ethnic Muslim Uighurs for the violence, but exiled Uighurs say police fired on students.
'Extraordinary defiance'
The BBC's Quentin Sommerville, on the streets of Urumqi, says at least 200 people - mostly elderly women or women with children - have taken to the streets, complaining that their relatives had been arbitrarily arrested.
Foreign journalists witnessed the protest during a tour led by government officials showing them parts of the city where shops and homes had been destroyed in Sunday's violence.
Our correspondent says it was an extraordinary act of defiance.
He says riot police - armed with rifles and tear gas - charged the women and surrounded them. But they sat on the ground in defiance of orders from policemen to disperse.
He says the protesters finally began leaving as the journalists were ushered away from the area.
But policemen were waiting in the side streets, he said, and it was unclear what had happened to the women.
Mass arrests
The mass arrests have been going on since Sunday's clashes.
Reports are surfacing that police have been going from house to house, rounding up young men for questioning.
The Chinese authorities say they have arrested the "ringleaders" of the protests, but that they are still seeking others.
In Urumqi's hospitals, the victims are still being treated, our correspondent says.
Many are reported to be ethnic Han Chinese, but there are Uighurs too and others from another Muslim ethnic group, the Hui.
Demonstrators said they had been demanding justice for two Uighurs killed last month in a fight with ethnic Han Chinese at a factory in southern China.
There has been widespread international concern at the clashes, which some analysts say are the most serious in China since Tiananmen Square in 1989.
UN Secretary General Ban Ki-moon led the calls for restraint, a sentiment echoed by Britain and the US.
