UPDATE (March 16): The Economist has an eyewitness account from their correspondent in Lhasa:
After hours of rioting on March 14th, a ring of troops was deployed around the large Tibetan quarter during the night. The next day some residents continued to attack the few Chinese-owned businesses still left intact. Your correspondent saw a group smashing the shutter of one shop and, in another alley, throwing looted goods into a huge fire. Smoke billowed up from an area where the city’s main mosque is located. Many ethnic Chinese in this part of Lhasa belong to the Hui, a Muslim minority, whose members control much of the city’s meat trade.
But as the security forces (in this area it appears they are mainly members of the paramilitary People’s Armed Police, a riot-control unit) continued to step up their presence, the rioting receded. At first some residents threw stones at those troops who were not armed with rifles, retreating rapidly when occasional tear-gas shells were fired. Later on Saturday, troops with rifles began moving into the alleyways, shooting single shots from time to time. Some traversed the rooftops of the densely packed, flat-roofed houses. One briefly appeared on the roof of your correspondent’s hotel, terrifying a Tibetan and two Westerners cowering below the parapet.
From Financial Times :
Chinese authorities have sealed Lhasa, the Tibetan capital, cutting off the city from visitors with a large military and armed police presence ahead of a “surrender deadline” of Monday at midnight.
The government has also tightened control over information coming out of the Himalayan region, blocking many Internet sites, including Youtube , which could be used to upload video content of the protests over the last week.
The protests began on March 10, when Buddhist monks staged protests against Chinese rule over Tibet, which China administers as a “special autonomous region”. Last week marked the 49th anniversary of the flight by the Dalai Lama, Tibet’s spiritual leader, to exile in Dharamsala, India.
Read also: Eyewitness accounts from Lhasa from the International Campaign for Tibet.