Tibetan monks in a Chinese region rocked by a deadly protest said Tuesday they were too afraid to leave their monastery where injured people had taken refuge, as hundreds of armed forces patrolled outside.

The increased security comes after police opened fire on Tibetans protesting against religious repression and as Chinese authorities sealed off another Tibetan-inhabited area which was also rocked by a demonstration, the London-based Free Tibet campaign group said.

Both protests took place in the southwestern province of Sichuan -- which has large populations of ethnic Tibetans, many of whom complain of a lack of religious freedom -- and where unrest has been on the rise over the past year.

In one of the protests Monday, rights groups and locals said at least one person died and more than 30 others were injured when police opened fire on Tibetans protesting in Sichuan's Luhuo county.

The local government confirmed in a statement that one protester was killed in a clash with police, but did not mention any shooting, the official Xinhua news agency reported.

A monk reached by phone Tuesday at the Dragko Monastery in Luhuo -- around one 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 reached by phone at a different time 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 home.

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

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

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

Xinhua had a different version of the incident, saying dozens of people gathered outside a bus station in Luhuo after a man put up posters claiming a monk would set himself on fire there.

It said the crowd started attacking a police station with clubs and stones. "One protester was killed in the following clash with the police, which also left five officers injured," it added.

A man at a hotel in Luhuo reached by phone said he heard three people had died in the unrest -- a toll that the US-based International Campaign for Tibet (ICT) also reached.

The India-based Tibetan government-in-exile, meanwhile, said six people may have died in the unrest.

Separately, on the same day, police fired tear gas into a crowd of Tibetans protesting against perceived oppression just under 300 kilometres away in Aba county, Free Tibet said.

"Additional security forces have been deployed in the area and roads connecting Ngaba (Aba in Chinese) to the surrounding counties have been closed by the authorities," the group said.

Calls to the Aba government and police went unanswered.

The protests add to already high tensions in China's Tibetan-inhabited regions, where 16 people have set fire to themselves in less than a year -- including four this month alone.

Many Tibetans in China complain of a lack of religious freedom and say 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.