Rioting erupted in a province neighbouring Tibet on Sunday, two days after violent protests by Tibetans against Chinese rule in Lhasa in which the region's exiled representatives said 80 people had been killed.
Tibet's spiritual leader, the Dalai Lama, said the Tibetan nation was in serious danger and called for an investigation into what he called cultural genocide in his homeland.
A police officer in Aba county, Sichuan, one of four provinces with large Tibetan populations, said a crowd of Tibetans had hurled petrol bombs in the main county town, burned down a police station and a market and set fire to two police cars and a fire truck.
"They've gone crazy," said the officer, her voice trembling down the telephone as the main government building there came under siege.
Security forces fired tear gas and arrested five people.
The Tibetan Centre for Human Rights and Democracy said on a Web site that paramilitary police shot and killed at least seven protesters. A police officer, reached by telephone, denied this.
One ethnic Tibetan resident in Aba said there were sounds like gunshots and there was widespread talk of 10 or more dead.
"Now it's very tense. There are police going round everywhere, checking and looking over people for injuries," said another Aba resident, adding that many of the rioters were students of a Tibetan-language high school.
Anti-riot troops locked down Lhasa -- remote, high in the Himalayas and barred to foreign journalists without permission -- to prevent a repeat of Friday's violence, the most serious in nearly two decades.
A businessman there, reached by telephone, said a tense calm had descended on the city and most people were staying indoors.
Xinhua news agency said the authorities had stopped granting foreigners tourist permits to visit Lhasa for their "safety".
"We also suggest foreign tourists now in Tibet leave in the coming days," Xinhua quoted Ju Jianhua, director with the region's foreign affairs office, as saying.
The Dalai Lama, the Nobel peace laureate who fled to India in 1959, called from his Dharamsala base in the Himalayan foothills for an investigation into the situation in Tibet.
