China has ramped up security in Tibetan areas, rights groups and residents said on Friday, after new self-immolation protests belied boasts of national unity at a key Communist Party congress in Beijing.

Six such incidents since Wednesday -- the eve of the gathering where the ruling party names its new leaders -- capped a recent escalation that marks the worst outbreak of Tibetan discontent since massive anti-China rioting in 2008.

Tibetan experts said the latest spate seemed timed to coincide with the congress and could prompt a further spiral of clampdowns and immolations, deepening the divide between Tibetans and authorities.

Armed police in paramilitary vehicles stepped up patrols in Tongren in the northwestern province of Qinghai after "thousands of protesters" took to the streets on Thursday, the UK-based Free Tibet group said in a statement.

"There are lots of police on the streets. They have increased their patrols and they stay out for 24 hours a day," a shop owner in the town centre who refused to give her name told AFP by phone.

Police in Tongren refused to comment when contacted by AFP.

Tibetan anger at Beijing's control has simmered for decades but burst out into violent riots against Chinese rule in the Tibet regional capital Lhasa and adjacent areas in March 2008.

The protests left 20 people dead, according to the government, while exiled Tibetans put the figure at 203, and prompted a massive security clampdown across Tibetan areas of southwestern China that remains to this day.

Tibetans' continued frustration has since been displayed by the immolations, in which 69 Tibetans have set themselves on fire since 2009, with 54 of them dying, according to the India-based Tibetan government in exile.

The situation is now a "vicious cycle" likely to plague China's stability-driven leaders indefinitely, despite Beijing's efforts to win over Tibetans by pushing economic development, said Tsering Shakya, a Tibet expert at the University of British Columbia in Canada.

"No matter how many Tibetans might protest, how many immolations might happen, the new Chinese leadership will not make any concession to the protesters," he said.

"They see that as a central issue of the authority of the Chinese government."

The spokesman for the Tibetan government in exile in India urged China to address Tibetan frustrations even while acknowledging that it would likely maintain its hard line and immolations would persist after this latest spike.

"The immolations are intended at sending out a strong message to the new leadership taking part in the Congress," said Lobsang Choedak, a view Shakya shared.

An 18-year-old man burnt himself to death on Thursday outside a monastery in Huangnan prefecture in Qinghai province, where a 23-year-old woman also died after setting herself alight on Wednesday, the India-based exile government announced.

A trio of young monks also set themselves alight on Wednesday in Aba County in Sichuan province, with one dying of his injuries, while another burning was confirmed in the Tibetan Autonomous Region on the same day.

China's leaders blame the exiled Tibetan spiritual leader the Dalai Lama -- who is deeply revered among Tibetans in China -- for fomenting unrest, a charge he denies.

"Conspiring to lead others to kill themselves is in and of itself criminal behaviour, and in Chinese law this constitutes the crime of intentional murder," Luosang Jiangcun, a member of the party committee overseeing Tibet and congress delegate, told reporters on Friday.

"The 'Dalai clique' sacrificing others' lives to achieve its own hidden political goals -- we believe this violates humankind's common understanding and morals".

Analysts say they fear that showing any weakness could embolden Tibetan protests and possibly spur other groups such as Muslim Uighurs in the far west region of Xinjiang to step up their demands.

Many Tibetans accuse the government of cultural and religious repression and are angry with the migration of majority Han Chinese to Tibetan areas.

China maintains that Tibetans enjoy religious freedom and improved living standards thanks to government investment in economic development.

Talks between China and representatives of the Dalai Lama broke down in 2010.