A Reuters picture showed a protester setting afire a Chinese national flag. Another depicted security personnel shielding themselves against rocks hurled by protesters.
Qiangba Puncog, the top government official in Tibet, told reporters in Beijing that Tibetan authorities had not fired any shots to quell the violence.
But official statements suggested the government reaction in coming days will be tough, and will bring Tibetan Buddhist monasteries and nunneries under tighter controls.
The Tibet government notice claimed that the burning of schools, hospitals, shops and houses was "premeditated". And an announcement on Tibet television urged residents to denounce the "malicious intent" of the Dalai Lama, "protect national sovereignty" and "reject lawless monks and nuns".
The International Campaign for Tibet cited unconfirmed reports of scores of Tibetans killed. John Ackerly of the group said in an e-mailed statement he feared "hundreds of Tibetans have been arrested and are being interrogated and tortured".
Danish tourist Bente Walle, 58, said Lhasa was like a ghost town on Saturday.
"Today Lhasa is completely closed and there is Chinese military all over," she said, adding that many people were tying white prayer scarves on doors. "The Tibetans put them on their doors to tell everybody: here is a Tibetan."
NO CHANGE OF POLICY
The riots emerged from a volatile mix of pre-Olympics protests, diplomatic friction over Tibet and local discontent with the harsh ways of the region's Communist Party leadership.
China has chided the leaders of the United States and especially Germany in past months for hosting the Dalai Lama, saying such acts boost what they call his "separatist" goals. It has also urged India to stop protests there by exiled Tibetans.
"We are fully capable of maintaining the social stability of Tibet," Xinhua quoted an official as saying in a statement repeated across Chinese state media on Saturday.
But already the protests have become an international issue dogging the Beijing Games, which China hopes will showcase its economic progress and social harmony.
Asked whether he thought the unrest in Tibet would affect the torch relay passing through there, Sun Weide, spokesman for the Beijing Organising Committee for the Olympic Games, said no.
"The preparations for the Torch relay in Tibet and taking the flame up Mount Qomolangma have been progressing smoothly," he said. Mount Qomolangma is better known as Mount Everest.
