A huge explosion rocked a chemical plant in eastern China on Thursday, killing at least six people and injuring dozens as it knocked down factory buildings, damaged homes and sent a huge plume of smoke skyward.

The windows of houses and a school in the surrounding area were shattered by the force of the explosion, and residents were evacuated, according to authorities and images published by local media.

The latest industrial incident to rock China in recent years occurred at around 2:50 pm (0650 GMT) at a facility run by Tianjiayi Chemical in Yancheng, Jiangsu province, city officials said on their official Twitter-like Weibo account.

Around the time of the explosion, China's earthquake administration reported a 2.2-magnitude tremor in Lianyungang, a city near the Yancheng blast.

An aerial view of the blast area showed a large swath of destruction in the industrial park, where multiple fires still raged as firefighters tried to douse them with hoses.

A CCTV reporter on the scene said that toxic fumes were coming from the blast site.

At least six people were killed and 30 seriously injured, while numerous others in the vicinity were slightly injured, city officials said on Weibo late Thursday.

‘At present, on-site rescue is still going on... The cause of the accident is under investigation,’ officials said.

Rescuers interviewed by CCTV repeatedly described the ground situation as ‘complex’, adding that the focus is still on trying to pull people from the site.

Injured residents near the site of the explosion have been sent to hospital for treatment, according to local authorities.

Medical staff, as well as personnel from the public security bureau and fire department, have been sent to the scene, they added.

- Buildings knocked down -

According to official news agency Xinhua, citing local authorities, the explosion occurred following a fire in a fertiliser factory in the chemical industrial park.

Workers near the site of the blast were trapped after shockwaves from the explosion knocked down nearby factory buildings, the report said.

Workers covered in blood were seen running out of the factory, Xinhua added, citing witnesses.

Images broadcast by state media showed an enormous explosion, with flames engulfing the top of the chemical plant while other shots showed thick grey smoke billowing skyward from the site of the blast.

Pictures from a local news outlet showed an classroom with blown out windows, children's backpacks scattered among broken glass and hastily abandoned schoolwork.

Strong winds around the site helped disperse fumes though there remain concerns about the toxicity of the fumes, Yancheng's environment bureau said in a later statement, adding that residents in the surrounding areas have been ‘basically evacuated’.

While there is a small river next to the site, there it is not used as a drinking source, the agency added.

- History of industrial disasters -

Industrial accidents are common in China, where safety regulations are often poorly enforced.

In November, a gas leak caused an explosion at a PVC production plant in a northern Chinese city that will host the 2022 Winter Olympics, killing 24 people and injuring 21 others.

A report published by local authorities in February revealed that the Chinese chemical firm responsible for the accident had concealed information and misled investigators.

Last July, a blast at a chemical plant in southwest Sichuan province left 19 dead and 12 injured. The company had undertaken illegal construction that had not passed safety checks, according to local authorities.

And in 2015, giant chemical blasts in a container storage facility killed at least 165 people in the northern port city of Tianjin.

The explosions caused more than $1 billion in damage and sparked widespread anger at a perceived lack of transparency over the accident's causes and its environmental impact.

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