More than 800 firefighters battled for almost 24 hours to put out a vast fire at a controversial chemical plant in the Chinese city of Zhangzhou, state media said Tuesday, the second accident at the site in two years.

The explosion and blaze came amid reports of a police crackdown on environmental protests in China's Inner Mongolia region some 2,200 kilometres away, sparked by waste discharged by local chemical plants onto grazing land.

Government officials in Inner Mongolia vowed to shut down several plants after the protests, in which thousands of police were said to have used tear gas and batons.

Large and sometimes violent protests against factories have become more common in China in recent years, where industry is a cause of widespread air, water and soil pollution.

Footage broadcast by CCTV News of the Zhangzhou blast showed flames billowing into the air following the explosion at the plant producing paraxylene -- a chemical commonly known as PX and used to make fabric -- in the eastern province of Fujian.

The explosion, said to have been triggered by an oil leak, occurred on Monday evening, with the official news agency Xinhua saying that witnesses reported feeling a tremor as far as 50 kilometres (30 miles) away.

Some 829 firefighters battled the blaze, the agency said, and it was put out after 21 hours.

No fatalities were reported, but conflicting reports put the number of injured at six or 19.

It was the second accident in 20 months at the plant, according to Xinhua.

Proposals for plants producing PX, a flammable and carcinogenic liquid used in the production of polyester films and fabrics, have sparked large protests in several Chinese cities in recent years over perceived health risks.

The Zhangzhou PX plant was originally slated to be built in the nearby coastal city of Xiamen, but was moved to its present site after thousands took part in a protest in 2007.

- 'Push out the chemicals' -

In Inner Mongolia, dozens of people were arrested at the weekend when around 2,000 police broke up demonstrations in Naiman Banner, a mainly rural region, according to the US-based Southern Mongolian Human Rights Information Centre (SMHRIC).

Pictures posted online showed people gathering on a countryside road beside an overturned police car, as well as dozens of riot police with shields and dogs. Used tear gas canisters lay on the ground.

One banner hanging over a roadblock read: "Push out the chemicals, give us back clean water and blue skies." The images could not immediately be verified.

SMHRIC on Monday cited residents as saying that a local "chemical refinery zone" had discharged waste directly onto grazing land used by members of the local Mongol minority in Naiman Banner.

"The police used batons to beat locals who were kneeling on the ground," a local man surnamed Feng told AFP, estimating that around 10 protesters remained in hospital.

SMHRIC cited a local woman as saying that one person had been killed in the protests. But the Naiman Banner government denied reports of any deaths.

"That's impossible. We never heard of that," a Naiman Banner official who declined to be named told AFP when asked about the reported death.

Local officials said in a social media posting Monday they had ordered all firms in the local "chemical zone" to cease production while it investigated.