Witnesses and residents in the Tibetan capital, Lhasa, say Chinese authorities have imposed a curfew and are battling flames lighting the night sky following Friday's protests.
Unconfirmed reports say several people were killed in clashes Friday between police and Tibetan demonstrators during protests that began peacefully and ended in violence. Witnesses report hearing gunshots fired in Lhasa's streets.
Rioters threw stones at police and set fire to shops, vehicles and the Chinese flag. Some reports say the attacks targeted shops owned by Han Chinese and Chinese muslims.
The protests, launched by Buddhist monks, are the region's most serious and prolonged demonstrations against Chinese rule since 1989. Chinese President Hu Jintao was then serving as Tibet's Communist Party boss and imposed martial law to halt protests.
An Indian-based human rights group says the protests have spread to Tibetan communities in neighboring Qinghai, Gansu and Sichuan provinces. Witnesses report that Chinese police fired shots to disperse a protest in Gansu province led by Tibetan monks from Labrang monastery.
Photographs show thousands of monks and other Tibetan protesters in the town of Xiahe, some carrying the banned Tibetan snow lion flag.
Chinese state media carried a report late Friday accusing supporters of Tibet's exiled spiritual leader, the Dalai Lama, of instigating Friday's protests across Lhasa.
A spokesman for the Dalai Lama called the allegation "absolutely baseless." The Tibetan spiritual leader had earlier issued an appeal for calm.
A spokesman from the London-based Free Tibet Campaign says protesters in Tibet are aware that the world's media is focused on China in the run-up to the Beijing Olympics.
Chinese security forces have surrounded Tibet's three largest monastic centers, Drepung, Ganden and Sera, on the outskirts of Lhasa. Some monks at Sera monastery are reported to have begun a hunger strike, while two monks at Drepung monastery reportedly attempted to commit suicide in protest.
The demonstrations began earlier this week, as Tibetans across the globe rallied to mark the 49th anniversary of the Tibetan uprising.
China has controlled Tibet since 1951. The Dalai Lama and thousands of his followers fled to India from Tibet in 1959 during a failed revolt against Chinese rule.
Some information for this report provided by AFP, AP and Reuters.