By Michael Bristow
BBC News, Urumqi
Armed police have set up roadblocks across central Urumqi
As dawn broke over western China, riot police took up their positions near the centre of Urumqi, using barricades to block off roads.
Some were armed with rifles and wore body armour; others carried shields and wooden batons.
Most were members of the People's Armed Police, a force charged with restoring order whenever unrest breaks out in China.
Tens of thousands of protesters staged angry protests on Thursday and the authorities seemed determined to prevent a repeat performance on Friday.
Schools and businesses were told to close while the current protests continue.
Despite that, some people were trying to carry on as normal.
"What are we supposed to do, stay at home?" said one of several traders who had set up their stalls in Urumqi's People's Square, alongside the riot police.
But other, angrier groups, mainly residents of Urumqi's Han Chinese ethnic group, soon started gathering on street corners in the city centre.
Thousands of people protested in Urumqi on Thursday
This led to angry words, pushing and shoving and fresh clashes.
China's state-run Xinhua news agency said tear gas was used to clear some crowds.
Riot police often managed to break up knots of people - but they soon gathered together again further down the street.
At one point, the crowd surged forward when a screaming woman was detained and pushed into a police van.
Call for justice
This was the third day of protests in Urumqi, the capital of Xinjiang, a resource-rich region that on paper enjoys a fair degree of autonomy from Beijing.
Residents are frustrated with the government's response to riots in July that left nearly 200 dead.
Most of those who died were Han Chinese, a group of people who have moved to Xinjiang in large numbers only in the last few decades.
They want the government to bring those responsible for the killings in July to justice - and they want them to do it quickly.
Some of the protesters on Friday shouted: "Down with Wang Lequan." He is Xinjiang's Communist Party secretary, the most important man in the region.
But this recent unrest appears to have begun when the government announced that many ordinary people had been stabbed with hypodermic needles.
It was unclear who was behind the attacks, but local residents told the BBC that this news had spread panic and fear among ordinary people.
"Before, I could walk around without being worried about being attacked. But now I walk like a thief - always looking around to make sure nobody is going to attack me. I just can't relax," one elderly woman said.
The authorities will sooner or later quieten the angry crowds and regain control of the city.
But the underlying ethnic tension behind the July riots will not simple go away, and will have to be dealt with if there is to be no more unrest in the future.
Are you in Urumqi? Have you witnessed or heard of the unrest? Send us your experiences using the form below.
A selection of your comments may be published, displaying your name and location unless you state otherwise in the box below.
The BBC may edit your comments and not all emails will be published. Your comments may be published on any BBC media worldwide.