A Tibetan father-of-three set himself on fire in China, prompting a large gathering of monks and lay people, rights groups said, as tensions in Tibetan-inhabited areas show no signs of abating.

Sonam Dargye, 43, died after setting himself on fire Saturday in Tongren in the northwestern province of Qinghai -- the third Tibetan to self-immolate in protest against Chinese rule in four days -- prompting a mass prayer vigil.

According to the London-based Free Tibet, thousands of Tibetans gathered in Tongren following the death of the farmer, with people pouring in from nearby villages, and armed police forces came to the scene but eventually withdrew.

The group said Sonam Dargye was a close friend of Jamyang Palden, a monk who set himself on fire in Tongren on Wednesday -- the fourth anniversary of deadly Tibetan unrest in 2008 -- and is believed to be critically ill.

The India-based Tibetan Centre for Human Rights and Democracy confirmed the latest self-immolation and subsequent gathering in Tongren, and said Sonam Dargye set himself alight "in protest against the Chinese government."

The government and police of Huangnan prefecture, which oversees Tongren, and restaurants, hotels and art centres in the city refused to comment when contacted by AFP.

One restaurant owner said calls were monitored, adding it was not "convenient" to talk, and it was unclear whether the gathering was still going on.

China's Tibetan areas have been hit by numerous bouts of unrest since the beginning of the year, as tensions over perceived repression boil over, but they have mainly been centred in the southwestern province of Sichuan.

However over the past week, neighbouring Qinghai has also witnessed unrest with the two self-immolations, subsequent gatherings and protests by students calling for freedom of language and equality, rights groups say.

Many Tibetans in China complain of religious repression, as well as a gradual erosion of their culture, which they blame on a growing influx of majority Han Chinese in areas where they live.

China, however, denies this and says Tibetans are leading better lives than ever before thanks to huge investment in infrastructure, schools and housing.