Officials demanded protesters turn themselves in, while baton-wielding police patrolled Lhasa's mostly empty streets on Saturday. Fires still smoldered from the Friday clashes, and residents were under curfew.
Reports of deaths, arrests and numbers of protesters varied and could not be independently confirmed.
China's official Xinhua News Agency said 10 people - including two hotel employees and two shop owners
- were burned to death, but that no foreigners were hurt. The exiled Tibetan government in India said about 100 were believed dead, citing unconfirmed sources.
Buddhist monks led the protests, which began Monday on the anniversary of a failed 1959 uprising against Chinese rule. The violent turn comes two weeks before China's Olympic celebrations kick into high gear with the start of the torch relay, which passes through Tibet.
Sun Weide, a spokesman for the Beijing Olympics organizing committee, said the unrest would have no negative impact on the Games or the relay.
"The hosting of the Beijing Games is the 100-year dream for Chinese people and I think the Chinese people, including our compatriots in Tibet, very much look forward to hosting the Games," Sun said.
Already the U.S. and other governments have urged China to show restraint toward the protesters, while International Olympic Committee President Jacques Rogge deferred, saying he didn't have details.
But a top official promised tough measures against detractors.
"We will deal harshly with these criminals in accordance with the law," said Champa Phuntsok, chairman of the Tibetan government.
"Beating, smashing, looting and burning - we absolutely condemn this sort of behavior. This plot is doomed to failure," said Phuntsok, an ethnic Tibetan, speaking on the sidelines of the National People's Congress, China's annual legislative session.
Law enforcement authorities in Tibet were offering leniency for demonstrators who surrender before Tuesday. Otherwise, they will be "severely punished," according to a notice carried on official Web sites and confirmed by prosecutors.
Phuntsok blamed the uprising on followers of the Dalai Lama, who fled into exile in 1959 after the failed uprising and is still Tibet's widely revered spiritual leader.
From Dharamsala, India, the headquarters of the Tibetan government-in-exile, the Dalai Lama appealed to China not to use force, saying he was "deeply concerned," and urged Tibetans "not to resort to violence."
It is extremely difficult to get independent verification of events in Tibet since China maintains rigid control over the area. Foreigners need special travel permits, and journalists are rarely granted access except under highly controlled circumstances.
But footage and photos sent from Lhasa showed plumes of smoke billowing from buildings and small shops scattered across several parts of the city. Fire trucks moved through mainly empty streets after dark.
Earlier, eyewitness accounts and photos posted on the Internet portrayed chaos in Lhasa on Friday, with crowds hurling rocks at security forces, hotels and restaurants. The U.S. Embassy said Americans had reported gunfire.
The violence came on the fifth day of what had been mostly peaceful protests against China's often harsh 57-year rule over Tibet. After police tried to stop monks from protesting in central Lhasa, ordinary Tibetans vented anger on Chinese, hurling stones and torching shops and cars.
"The protesters yesterday went from attacking Chinese police to attacking innocent people very, very quickly," said a blog entry by a group of Westerners staying in a hotel in central Lhasa near the riot. "Many Tibetans were also caught in the crossfire."
Video footage on the web site showed Tibetan looking men attacking a motorcyclist, hitting him with rocks and pushing him over.
On Saturday, Xinhua said Lhasa had "reverted to calm."
"There was not much traffic on the road," the Xinhua report said. "Burned cars, motorcycles and bicycles remained scattered on the main streets, and the air is tinged with smoke."
Some shops were closed but government staff were required to work, said a woman who answered the telephone at the Lhasa Hotel.
