Authorities in Tibet and restive parts of western China were on heightened alert Tuesday for possible unrest on the 50th anniversary of a failed uprising against Chinese rule as the Dalai Lama said Tibet had become "hell on earth" under Beijing's control.

In a speech marking the anniversary of his flight from China, the exiled Tibetan spiritual leader said decades under Chinese martial law and hard-line policies such as the Cultural Revolution had devastated the Himalayan region, leading to the deaths of hundreds of thousands of Tibetans.

"Even today, Tibetans in Tibet live in constant fear and the Chinese authorities remain constantly suspicious of them," he said from his home in Dharmsala, India, denouncing the military's "brutal crackdown" in Tibet after anti-Chinese protests broke out a year ago.

After the Dalai Lama's speech, thousands of young Tibetans took to the streets in Dharmsala, chanting "China Out!" and "Tibet belongs to Tibetans!" Protesters also held marches in support of the Tibetans in New Delhi, Seoul and Canberra, Australia.

Tibet governor Champa Phuntsok said Tuesday the Dalai Lama's claims about Tibetan deaths was "merely fabrication and vilification," according to the official Xinhua News Agency. Tibet's population has grown very rapidly in the past 50 years, increasing from 1.2 million in 1959 to 2.87 million in 2008, he said.

Beijing had sought to head off trouble on the anniversary that marked the start of the 1959 abortive Tibetan revolt against Chinese rule. A peaceful commemoration last year by monks in Lhasa, Tibet's regional capital, erupted into rioting against Chinese rule four days later and spread to surrounding provinces — the most sustained and violent demonstrations by Tibetans in decades.

On Tuesday, residents and businesses in the regional capital of Lhasa reported seeing increased patrols of armed police throughout the city.

"There are more paramilitary police in the streets. They're at bus stations, road intersections, even small alleys," said a staffer at the West Tour Go tourism agency in the capital, who declined to give his name.

In neighboring Sichuan's Ganzi prefecture, where some of the most violent protests occurred last year, rows of riot police and soldiers with machine-guns marched through the middle of Kangding town past the main square.

The night before, local Communist Party official Xiang Luo had exhorted paramilitary troops to be especially vigilant: "You must do this month's work well. This is crucial."

Officials there said the provincial government had issued an emergency notice Monday ordering foreigners — including reporters — out of the mixed Chinese-Tibetan town. Kangding, known for its strong sense of Tibetan identity, had been the last corner of Ganzi to remain open.

The security cordon around the entire region has tightened with increased controls at Tibet's border points and main highways to prevent disruptions by supporters of the Dalai Lama, China's public security ministry said.

In Tsedang, Tibet's third-largest town, two hours southeast of Lhasa, a staffer at the Shannan Yulong Holiday Hotel said the heightened security has been in place since last week.

"Police come to check out our registration for people staying in the hotel every day ... Even though it seems relatively quiet, we can feel that the security is very tight now," said the staffer, who declined to give a name for fear of reprisals.

This year, chains of police checkpoints confronted travelers to ethnically Tibetan areas — a quarter of Chinese territory that stretches from Tibet to parts of Qinghai, Sichuan and Gansu provinces. Convoys of armored vehicles and sandbagged sentry posts have turned the remote mountainous region into something of an armed camp. Police patrols have increased outside Buddhist monasteries.

On Monday, China's President Hu Jintao said Tibet was basically stable and urged Tibetan politicians in Beijing to develop the region economically to clamp down on separatism.