China on Tuesday accused "overseas secessionist groups" of trying to discredit the government after a deadly clash in a Tibetan-inhabited area saw injured locals taking refuge in a monastery.

According to the London-based Free Tibet advocacy group and local monks, police opened fire at Tibetans protesting against religious repression in the southwestern province of Sichuan on Monday, killing at least one and injuring over 30.

But China's foreign ministry said Tuesday their account of the incident in Luhuo county was hyped, and that a mob stormed stores and a police station, prompting a clash in which one protester died and five officers were injured.

"Overseas forces of 'Tibet independence' have always fabricated rumours and distorted the truth to discredit the Chinese government with issues involving Tibet," spokesman Hong Lei was cited as saying by the state Xinhua news agency.

The unrest comes at a sensitive time in Tibetan-inhabited areas, where at least 16 people have set fire to themselves in less than a year -- including four this month alone.

In a sign of widespread tensions in these areas, a separate protest also rocked Sichuan's Aba county -- home to many ethnic Tibetans -- on Monday, prompting police to fire tear gas at a crowd of demonstrators, Free Tibet said.

A monk reached by phone Tuesday at the Drakgo Monastery in Luhuo -- around a kilometre (half a mile) from the scene of the protest -- said he estimated around 1,000 to 2,000 armed police were now standing guard.

"We are treating 32 injured people inside the monastery, and two of them are critical. One of them has a bullet in the head," the monk, who would not be named, told AFP.

Another monk said they were too afraid to take the wounded to an outside hospital due to the strong security presence, adding those protesting on Monday had now gone but the number of armed forces kept increasing.

"More police are coming, we just want peace," he said.

The government and police in Luhuo refused to comment when contacted by AFP.

Accounts of the death toll vary. The monks and Chinese government say one person died, but a man at a local hotel said he heard three people had been killed, as did the US-based International Campaign for Tibet (ICT).

The India-based Tibetan government-in-exile, meanwhile, said the death toll could be as high as six.

According to monks reached by phone on Monday evening, the shooting happened after thousands of people marched to the local police station to call for religious freedom and to protest against local corruption.

Xinhua, however, said more than 100 people gathered in Luhuo due to rumours that three monks would self-immolate there, and the clash ensued.

Both Free Tibet and ICT cited sources as saying anonymous people had put up posters that declared a Tibetan would self-immolate.

Hong said the situation had now returned to normal. "Local authorities have been conducting an investigation into the incident," he was quoted as saying.

According to Stephanie Brigden, head of Free Tibet, the unrest in Luhuo was "the largest reported shooting of Tibetans since 2008 and demonstrates the deepening crisis in Tibet."

She was referring to riots that erupted in Lhasa -- capital of the Tibet autonomous region that neighbours Sichuan -- in March 2008, prompting a wave of protests in nearby Tibetan-inhabited areas over the following months.

The group said many security forces had been deployed in Aba -- some 270 kilometres away -- after the Monday protest there "and roads connecting Ngaba (Aba in Chinese) to the surrounding counties have been closed by the authorities."

Calls to the Aba government and police went unanswered.

The tensions in Tibetan-inhabited areas stem from complaints of a lack of religious freedom, with many Tibetans also saying their culture is being eroded by an influx of majority Han Chinese in the areas they live in.

But Beijing denies it uses repressive methods against Tibetans, insisting they enjoy freedom of religious belief and that huge ongoing investment into Tibetan-inhabited areas has greatly raised their standard of living.

It blames much of the unrest in Tibetan-inhabited regions on the Dalai Lama, a Nobel Peace Prize winner who fled Tibet in 1959 following a failed uprising against Chinese rule and who is vilified by China as a "separatist".