Police fired tear-gas and beat demonstrators who stormed government buildings in southern China on Tuesday to protest against a power plant, witnesses said, in the latest violent unrest to hit the country.

Residents of Haimen, a town in the province of Guangdong, are demanding the coal-fired plant be moved, saying it is damaging their health, demonstrators told AFP by telephone.

They said a 15-year-old boy had been killed and more than 100 others badly beaten by riot police, although this could not be independently confirmed.

AFP calls to the local government in the town of Haimen went unanswered. A woman contacted by telephone at the local public security bureau denied there was unrest in the town.

Haimen is only around 115 kilometres (70 miles) northeast of Wukan village, where residents are in open revolt against the local government after what they say is years of illegal land grabs.

There is no indication that the protests are related, but they are part of an upsurge in social unrest in Guangdong, China's wealthiest province and the country's manufacturing hub.

Photos posted online purportedly of the protest scene showed dozens of police armed with batons and shields lined up along a stretch of road.

Other photos showed protesters surrounding a government building with dozens standing on the roof of the entrance.

"They are still firing tear gas right now, lots of people are crying and they are on the ground," a protester told AFP, estimating that 100 to 200 riot police had confronted residents.

"If they continue, we will come out tomorrow and keep protesting. They are starting to beat people now," he said, before hanging up.

Another demonstrator told AFP that 10,000 residents had blocked a highway into the town to "get attention" after the local government refused to see them.

"We are protesting because we want the power plant to move away. Lots of local people have illnesses such as cancer," a resident said.

State media reported last month that a 7.4-billion-yuan ($1.17-billion) expansion of a power plant in Haimen had failed environmental tests.

Toxic metals found in local waterways, such as lead, zinc and nickel, "exceeded the standard level", Caixin said.

Three decades of rapid economic growth have left most waterways in China severely contaminated and protests over environmental pollution are increasing.

The villagers of Wukan are threatening to march on government offices on Wednesday if their demands for the release of three community leaders and the body of a fourth, who died in police custody, are not met.

Villagers also want a full investigation into what they say are years of illegal land grabs that has cost many local farmers their livelihood.

The recent outbreak of unrest will be a key concern for stability-obsessed leaders in Beijing as they prepare for a once-in-a-decade transition of power that begins next year.

Despite attempts to censor the web and a virtual black-out in China's state-run media, weibos -- Chinese microblogs similar to Twitter -- have buzzed with news of the Haimen and Wukan protests.