Tibet's exiled government on Thursday said it was seriously concerned by continued self-immolations in protest against Chinese rule of the Tibetan plateau and urged world leaders to "end the crisis".

The statement came after rights groups said two teenagers burned to death in southwest China this week, taking to over 50 the number of Tibetans who have set themselves alight in protest against Beijing's rule.

The Central Tibetan Administration, headquartered in the northern Indian hill town of Dharamshala, said in a statement it was "gravely concerned by the deteriorating situation in Tibet."

"We appeal to individual governments to use their good offices to engage the Chinese government to end the crisis in Tibet at the upcoming United Nations General Assembly meeting in September," the Tibetan government said.

"Over 51 Tibetans have now set themselves on fire in protest against the Chinese government's repressive policies," the leadership added.

Lobsang Kalsang, 18, a Buddhist monk, and former monk Damchoek, 17, died in hospital on Monday after setting themselves on fire in Aba town, which has become a flashpoint for such protests by ethnic Tibetans.

China's Tibetan-inhabited areas have seen an explosion in the violent form of protest since March 2011 when the self-immolation of a monk named Phuntsog at Aba's revered Kirti monastery sparked riots and a police crackdown.

Experts say suicide is a major taboo in Tibetan Buddhist culture, and the immolations are a sign of growing desperation among those living in the vast and remote Tibetan plateau.

The exiled leadership said the whole of Tibet was under "undeclared martial law".

The Central Tibetan Administration urged Beijing to allow a fact-finding delegation and international media to visit Tibet and to pursue a "substantive dialogue" to resolve the issue.

Tibetans have long chafed under China's rule over the Tibetan plateau, saying Beijing has curbed religious freedoms and their culture is being eroded by an influx of Han Chinese, the country's main ethnic group.

China has accused the Dalai Lama -- who fled Tibet to India following a failed uprising against Chinese rule in 1959 and is vilified as a "separatist" by communist authorities -- of encouraging the protests.

The Dalai Lama has condemned self-immolations and blamed them on the hardline Chinese rule of Tibetan-populated areas.

"The responsibility for the tragic self-immolations in Tibet lies entirely with the Chinese government, so does the solution," the exiled government said.