SHANGHAI — Fresh ethnic violence has erupted in a Tibetan region of southwestern China, with disputed reports of eight people shot dead by the police, and the Chinese government on Friday vowed swift and severe punishment of Tibetans accused of rioting and taking part in last month’s antigovernment protests.

Police officers fired Thursday evening on a crowd of protesters outside government offices in the Garze Tibetan Autonomous Prefecture in Sichuan Province along the border with Tibet. A Tibet activist group said the shooting left eight protesters dead, according to The Associated Press.

Signs of ethnic unrest in another area, in the northwestern region of Xinjiang, have also begun to emerge in recent days, with details of protests and rumored plotting by Muslim separatists in the Xinjiang Uighur Autonomous Region and of police crackdowns in several areas of the region.

China’s official Xinhua news agency confirmed the latest incidence of Tibetan unrest in Sichuan Province, saying that a riot had broken out and that the “police were forced to fire warning shots to put down the violence,” citing a local official. It said a government official was attacked and seriously injured in the protest, but gave no details of other injuries or deaths.

The pro-Tibet activist group, the London-based Free Tibet Campaign, said hundreds of Buddhist monks and lay people had marched on the government offices to demand that two monks detained for possessing photographs of the Dalai Lama, the exiled Tibetan spiritual leader, be released, The A.P. reported.

In an interview with Reuters, Dilxat Raxit, spokesman for the World Uighur Congress, a Germany-based exile group that seeks independence, said the authorities were using the Olympics as an excuse to crack down on the Uighurs. “One world, one dream?” Mr. Raxit said, referring to Beijing’s Olympic motto. “Is that right? The Uighurs have a different dream. We don’t want the Olympics here.”