Dramatic video footage that purportedly captures the moment a Tibetan Buddhist nun burned herself to death in southwest China has emerged after it was smuggled out and given to a campaign group.

The video, which AFP cannot independently verify, was posted online by Students for a Free Tibet and shows a figure being engulfed in flames in the middle of a street before collapsing to the ground.

The group says the figure is Palden Choetso, a 35-year-old Buddhist nun who self-immolated on November 3 in a Tibetan-inhabited town in Sichuan province.

The Tibetans shown in the footage had "risked everything" to smuggle it out of China, said Tenzin Jigdal, programme director of Students for a Free Tibet, which has offices in New York and Dharamshala, the Indian town that is home to the Tibetan spiritual leader the Dalai Lama.

The video released by the group also shows Tibetan Buddhist clergy gathering to mourn the nun's passing, as well as Chinese security forces converging on the Tibetan monastery where the funeral was held.

China's state-controlled Xinhua news agency was the first to report the incident in Sichuan's Ganzi prefecture, identifying Palden Choetso by her Chinese name, "Qiu Xiang."

She was the second nun to burn herself to death in Sichuan, a province with a large ethnic Tibetan population that has seen protests against what some see as growing domination by China's majority Han ethnic group.

Nine Tibetan monks have also attempted to burn themselves to death this year and rights groups say at least five have succeeded.

China, which has invested heavily in development in the remote Himalayan region, maintains that it has brought modernisation and a better standard of living.

"This footage shows not only the desperation but also the determination of Tibetans to fight for their freedom at any cost," Tenzin Dorjee, director of Students for a Free Tibet, said in a statement.

"We fear the situation will continue to escalate and more Tibetan lives will be lost if the Chinese government does not lift its repressive measures and commit to a just and lasting resolution to this spiralling crisis in Tibet."