Shops were set on fire in violence in Tibet's capital of Lhasa on Friday, China's Xinhua news agency reported after days of rare street protests in the contested region.
Witnesses said a number of shops were burnt, the report said.
Hundreds of people had taken to Lhasa's streets again on Friday in defiance of Chinese authorities and despite a heavy police presence and reports of a lockdown on monasteries, according to other sources.
Chinese rule in the remote, Buddhist region has become a focus for critics ahead of the Beijing Olympics, with global marches this week to mark the 49th anniversary of a failed uprising against Communist rule spilling into Tibet itself.
"The police are everywhere," said one cafe owner reached by phone in Lhasa. "There are big problems."
On Friday, 300 to 400 residents and monks demonstrated in Lhasa, a source cited a witness as saying, capping a week of daily protests led by the Buddhist clergy, an echo of the anti-government protests that rocked neighbour Myanmar last year.
"Some are angry and some are scared. The security forces are checking houses to see if any monks are hiding," said the source, who is in touch with Tibetan residents.
More than 10 monks had been arrested and tanks were patrolling the square near the Potala Palace, the person said, refering to one of the architectural wonders of the world, the one-time winter residence of Tibet's spiritual leader, the Dalai Lama.
This week's shows of defiance are precisely what the Chinese government has been trying to avoid as it seeks to secure a stable environment for the Games, which open on Aug. 8.
The region has been periodically restive since Chinese troops invaded in 1950. Nine years later, the Dalai Lama staged a failed uprising against Chinese rule and fled into exile in India.
On Monday, 500 monks from the Drepung monastery marched in Lhasa. That was followed by action from monks at the Lhasa-area Sera and Ganden monasteries. Security personnel fired tear gas on at least one of the demonstrations, reports said.
The Washington-based International Campaign for Tibet said authorities had sealed off all three monasteries.
"All three monasteries are closed off to tourists," the group said in a statement, citing tourism operators. "There is an intensified atmosphere of fear and tension in Tibet's capital."
The US-government-funded Radio Free Asia (RFA) reported monks from Sera were on a hunger strike, demanding withdrawal of Chinese paramilitary forces from the monastery compound and the release of monks detained earlier this week.
Two monks from Drepung were in critical condition after attempting suicide by slitting their wrists, RFA said.
The number of Tibetans detained could not be confirmed, but the watchdog groups said they expected government reprisals.
"There are indications that the authorities have begun a process of investigation in monasteries that could lead to detention and torture," the International Campaign for Tibet said.
New York-based Human Rights Watch called on China, as well as Nepal and India, which have seen similar demonstrations, to release detained Tibetans. (Reuters)
Shops set on fire in week-long Tibet unrest