Security is tight in Urumqi in China's Xinjiang region ahead of the first anniversary of deadly ethnic riots.
Armed police have been deployed in the city and thousands of "riot-proof" CCTV cameras set up in public places.
A government-run website said that all police leave had been cancelled.
The violence that erupted on 5 July 2009 between Uighur Muslims and Han Chinese was the region's worst ethnic violence in decades. Almost 200 people were killed.
Clashes ended after huge numbers of troops were deployed in the remote western region.
After the riots, the government suspended the region's communication links to the rest of the world, including international phone calls, text messaging and the internet.
Local tensions
Witnesses reported a heavy police presence on the streets of Urumqi on Sunday ahead of the anniversary.
All holidays had been cancelled for Urumqi police officers between 20 June and 20 July, a government-run website said.
Some 5,000 police officers have been recruited in Xinjiang since the clashes, China's state media reported.
Urumqi's police chief Wang Mingshan said officers had been staging drills to deal with any emergencies.
Surveillance cameras in protective casing had been put up in stations, schools and shops, and were being monitored around the clock, Xinhua news agency said.
China has blamed last year's violence on the local ethnic Uighur population, saying most of the recorded dead were Han Chinese.
But Amnesty International has challenged the official Chinese version of events, saying police used unnecessary force against Uighurs, followed by mass arrests and torture.
More than eight million Uighurs live in Xinjiang, which borders Central Asia.
Many are unhappy about the large influx of Han Chinese settlers which they say has increasingly marginalised their interests and culture.
