According to reports, witnesses saw "flashes of fire and heard sporadic gunshots after the explosions" in Kucha. The oasis city is on the northern rim of the Taklimakan Desert.
Xinhua news agency said, "The lawbreakers drove a taxi to the local public security office, industry and business administration and other sites and tossed homemade explosives, destroying two police vehicles." Five attackers were shot dead by police, and two police and a security guard were injured, it said.
A separate English-language Xinhua report said two people "were known to have been killed in a series of explosions" in Kuqa, but was unclear whether those deaths were in addition to the five attackers killed.
Local officials contacted could not or refused to clarify how many died and how, Reuters said.
"The circumstances are still unclear...Our leaders haven't determined the nature of the incident yet," said an official in the Kuqa Communist Party Committee office. He refused to give his name. "It looks like separatist forces," he said when asked.
Last week, only four days before the opening of the Olympics, a border post in the region was attacked and 16 policemen were killed. Two persons drove in
a rubbish truck and threw two grenades, before setting upon the policemen with knives. Both attackers were captured subsequently during a raid near the city of Kashgar, near the border with Tajikistan.
Xinjiang is home to the ethnic Uighurs, a Muslim minority in the country that has long chafed under Chinese rule. A group calling itself the Turkestan Islamic Party, an underground separatist organization, has threatened to stage attacks during the Olympic Games to draw attention to its demands for the region's independence.
On Saturday a US tourist was stabbed to death and a
second one was badly hurt in the attack at the Drum Tower monument in central Beijing, a popular tourist attraction, 5 km from the main Olympics site.
The assailant then committed suicide by jumping from the 13th Century landmark and his targets happened to be relatives of a US volleyball team coach.
Officials named the Chinese man as 47-year-old Tang Yongming, from the eastern town of Hangzhou, but said they had no idea what had motivated his attack or suicide.
Even as the authorities were dismissing the attack as a one-off and were stressing tourists were safe in the national capital, fresh irruptions have been reported in Xinjiang. Though it is some 4,000 km away from Beijing, it is still a huge embarrassment to the government.
The run up to the Olympics itself was bedeviled by riots in the Tibetan region, fierce demonstrations during the torch relay, concerns over air pollution and finally the terrible earthquake.
Still the authorities have sought to put up a brave face, and the opening was indeed a grand spectacle.
Beijing is under a tight blanket of security. In addition to 80,000 police officers, 100,000 anti-terrorism troops are mobilized and 300,000 surveillance cameras have been placed throughout the city. The army said it is flying unmanned drones to increase surveillance and have placed Hongqi 7 air-to-ground missile batteries near Olympic venues.
Nevertheless many are becoming nervous.
Last week, a senior Chinese army officer had warned that Islamic separatists were the biggest danger to the Olympics, it may be recalled.