One person died and 50 were arrested after some 2,000 police, using rubber bullets, tear gas and water cannons, put down a protest by villagers against pollution from a chemical plant in China’s Inner Mongolia, an overseas human rights group said.

Inner Mongolia has seen sporadic unrest since 2011 when the vast northern region was rocked by protests after an ethnic Mongol herder was killed by a truck after taking part in demonstrations against pollution caused by a coal mine.

Ethnic Mongols, who make up less than 20 percent of Inner Mongolia’s 24 million population, say their grazing lands have been ruined by mining and desertification and that the government has tried to resettle them in permanent houses.

Coal rich Inner Mongolia is supposed to enjoy a high degree of self-rule, but many Mongols say the Han Chinese majority has been the main beneficiaries of economic development.

In the latest incident, villagers in Naiman Banner took to the streets to protest against a chemical processing zone they said was polluting farmland and grazing land, the New York-based Southern Mongolian Human Rights Information Centre said in a statement late on Monday.

The group quoted a witness as saying police used rubber bullets, tear gas and water cannons to disperse the demonstrators, leading to one death.

An official who picked up the telephone at the local government said he was unable to confirm any deaths and declined to comment further.

However the government posted on its official microblog on Monday that it had ordered the chemical zone to close and shift to another undisclosed location and that it would punish any rule breaking by the companies there.

The government also said that it would go after protesters who blocked roads, smashed up vehicles, stoked tension or spread rumours.

About 90,000 "mass incidents" - a euphemism for protests - occur each year in China, triggered by corruption, pollution, illegal land grabs and other grievances.

Aware at the anger over environmental problems, the Chinese government has declared a war on pollution, vowing to abandon a decades-old growth-at-all-costs economic model that has spoiled much of China’s water, skies and soil.