The deadline for Tibetan protesters to surrender to the police has passed, after a quiet day in the city of Lhasa.
China had given demonstrators in the city until midnight (1600 GMT) to give themselves up or face punishment.
Exiled Tibetans said security forces had been rounding up political dissidents and witnesses said there was a heavy police presence on the streets.
Dozens are feared dead after days of rioting in Lhasa, with each side accusing the other of excessive force.
Other parts of China also saw rallies on the weekend, while Tibetans in Nepal and India are continuing to protest.
Qiangba Puncog, the Tibetan regional governor, said earlier that 13 "innocent civilians" had been killed by mobs in Lhasa.
He blamed the unrest on outside forces including Tibet's spiritual leader the Dalai Lama, who heads the Tibetan government-in-exile from India.
"The Dalai group and some other people in Western countries look at the beating, burning and smashing activities in the riots in Lhasa as peaceful demonstrations," he said.
"No democratic country in the world will tolerate this kind of crime."
The exiled Tibetan government says at least 80 protesters died in the Chinese crackdown.
Spokesman Tenzin Takhla said the security forces had regained control of the city and it was impossible for anyone to hold a rally there at the moment.
He said there were house-to-house searches going on and a number of former political prisoners were reported to have been detained again.
One Lhasa resident told the BBC late on Sunday that there was a heavy police presence in the city - but signs of normal life had returned.
"The schools are now open and children are going to school but shops are still closed as lots have been damaged and burned," he said.
Rocks hurled
Meanwhile, in neighbouring Sichuan province, rights groups say seven people were killed when security forces opened fire on Tibetan protesters in the city of Aba on Sunday.
And in Machu, Gansu province, a protester told the BBC a crowd of people set government buildings on fire on Sunday.
Groups of people also took down the Chinese flag and set it on fire, replacing it with the Tibetan flag, he said.
Smaller protests were reported elsewhere in Gansu and Tibet.
China has given Tibetans involved in the Lhasa protests a deadline of midnight on Monday local time to surrender to police.
The Dalai Lama has called for an international inquiry into China's crackdown, while Western leaders have called for restraint.
Anti-China rallies began on 10 March - the anniversary of a Tibetan uprising - and gradually intensified.
On Friday, demonstrators in Lhasa set fire to Chinese-owned shops and hurled rocks at local police, triggering a crackdown.
The unrest comes as preparations for this year's Olympic Games in Beijing are well advanced.
China has already faced calls for boycotts over its policies in Africa, and Olympic chief Jacques Rogge said he was "very concerned" about the situation in Tibet.
But the European Union's 27 sports ministers have dismissed the idea of a boycott over Tibet.
Pat Hickey, president of the European Olympic Committee, said: "Boycotts have never worked... the only people who are punished in a boycott are athletes."
China says Tibet has always been part of its territory. But Tibet enjoyed long periods of autonomy before the 20th Century and many Tibetans remain loyal to the Dalai Lama, who fled in 1959.
