Authorities Wednesday ordered foreigners to leave the riot-torn Tibetan capital of Lhasa, while Chinese troops acting under a new martial law decree began sealing off the city in a bid to prevent futher unrest.

No new violence was reported in the Himalayan region Wednesday, one day after the Chinese government declared martial law following the worst unrest in Tibet in three decades.Official reports said 12 people died and more than 110 were wounded in rioting that began Sunday, but foreigners in Lhasa estimated the death toll as high as 50. Chinese officials have given lower casualty tolls than reliable foreigners in three previous major disturbances in Tibet since October 1987.

The government declared martial law in the region at midnight Tuesday and sent People's Liberation Army soldiers to back up police and paramilitary units. Troops armed with automatic weapons patrolled Lhasa streets Wednesday.

Foreigners reached by telephone in Lhasa said authorities had ordered tourists to leave the city by noon Thursday. Western diplomats have estimated the number of tourists still there at 50 to 100, although some have left since the violence began.

Guy Dinmore, a Beijing-based correspondent who was in Lhasa for the British news agency Reuters, was held overnight for questioning by local officials and then ordered to remain in his hotel pending investigation of his presence in the Himalayan region, the agency said.

Foreign reporters in Beijing are required to apply for permission to travel to regions outside the capital for work and to give local officials 10 days advance notice of travel plans.

Long said foreign teachers who are under contract and businessmen with permanent offices will be allowed to remain in Tibet.

Foreign diplomats based in Beijing said they had been advised by the Chinese Foreign Ministry that a note would be issued Thursday to foreign embassies barring travel to Tibet by diplomats for the duration of martial law.

Foreigners reached in the Sichuan Province capital of Chengdu, the nearest major Chinese city to Tibet, said travel agencies had stopped selling tickets to Lhasa, but that some tourists were still attempting to get on flights to the city.

Telephone communications were intermittent with Lhasa, but telex lines were still operating Wednesday.

The ban on foreign travel and martial law orders that effectively sealed off Lhasa raised concerns an intense crackdown might ensue before Friday's 30th anniversary of a March 10, 1959, armed rebellion by Tibetans that was crushed by Chinese troops.

The anniversary of the rebellion, which forced the Tibetan spiritual leader, the dalai lama, into exile, has been seen as a possible flashpoint for more violence.