Hundreds of people have been arrested across Tibet in a crackdown by Chinese authorities following deadly riots in the region and neighbouring provinces, activist groups said on Wednesday.
"It seems like there are so many hundreds of arrests at least, possibly thousands, across the country (wider Tibetan region)," Lhadon Tethong, director of Students for a Free Tibet, told AFP.
"We cannot keep up at this point... there is such a flood of information."
Kate Saunders, from International Campaign for Tibet which has close contacts in Lhasa, also said there had been many arrests in the capital.
"In Lhasa we (have been told about) hundreds of arrests," she told AFP.
Human Rights Watch said in a statement it had unconfirmed reports of hundreds of arrests and warned those in custody were in great risk of being tortured.
No one was immediately available for comment at the Tibetan or Lhasa government. A male official with the public security bureau in Lhasa would not comment on the surrenders or the arrests and told AFP to stop calling.
Journalists have been prevented from getting access to any of the areas where riots and violence have been reported.
Chinese authorities said 105 "rioters" involved in protests in Lhasa had surrendered, the official Xinhua news agency reported on Wednesday.
Chinese authorities said rioters killed 13 "innocent civilians" in Friday's unrest in Lhasa, when a week of protests by Tibetans against China's rule of their homeland erupted into violence.
Authorities have insisted that they did not use any lethal force to quell the protests, however exiled Tibetan leaders have said possibly hundreds of people were killed in the ensuing Chinese crackdown.
Other unrest has been reported in neighbouring Sichuan, Qinghai and Gansu provinces which have ethnic Tibetan populations.