A Tibetan youth has burned himself to death in southwestern China, the third self-immolation in three days, in what overseas Tibetan rights groups said reflects growing resentment against China's policies in the Tibetan areas.

Dorjee, 18, died after he set himself ablaze in Aba county in Sichuan province on Monday in protest at China's policy on Tibet, human rights organisations Free Tibet and International Campaign for Tibet said .

A local official and police told Reuters by telephone that they had no knowledge of the incident.

Dorjee was the 25th self-immolation in the past year, with at least 18 believed to have died from their injuries, according to rights groups.

The latest deaths were all ordinary people and not, as is often the case, Buddhist monks or former clergy.

Isabel Hilton, editor of the London-based China Dialogue, said the string of self immolations was a measure of despair in response to an intensification of Chinese policies.

“This is certainly the most widespread and consistent protest since 2008. And the interesting thing about it is that although it began with religious community, monks and nuns, it has spread way beyond that," she said.

"And it has spread into places that was not traditionally close to the Dalai Lama."

Free Tibet, based in Britain, cited an eyewitness saying Dorjee set himself on fire near a bridge and then walked in flames to a government office building where he collapsed.

Tibetan monks at the Kirti monastery in India's Dharamsala, the seat of the Tibetan government-in-exile, said Dorjee shouted slogans against the Chinese government's policies on Tibet as he set himself ablaze, according to the US-based International Campaign for Tibet.

Dorjee's death came two days after two Tibetans killed themselves by setting themselves on fire in Sichuan and neighbouring Gansu province.

"This third self-immolation in as many days underlines that Tibetans will not stop protesting until their calls for freedom are heeded," Stephanie Brigden, the director of Free Tibet, said in an emailed statement.

"The international community must take immediate action."

Activists say China violently stamps out religious freedom and culture in Tibet, the mountainous region of western China which has been under Chinese control since 1950.