The death toll from a massive explosion at a chemical plant in eastern China has risen to at least 64, with hundreds of others injured, 90 of them seriously.

Key points: State-run television showed crushed cars and factory workers with bloodied heads

State-run television showed crushed cars and factory workers with bloodied heads Windows shattered in buildings up to 6 kilometres away

Windows shattered in buildings up to 6 kilometres away Last year 13 safety hazards were discovered at the factory

Rescuers pulled a survivor from rubble early on Saturday (local time), more than 24 hours after the blast at the factory, which had a long record of safety violations.

The number of deaths appeared likely to rise still further, with another 28 people still listed as missing, the official Xinhua News Agency reported.

Just 26 of those confirmed dead in Thursday's explosion have been identified, it said.

The blast in an industrial park in the city of Yancheng, north of Shanghai, was one of China's worst industrial accidents in recent years.

State-run television showed crushed cars, blown-out windows and workers leaving the factory with bloodied heads.

Fire burns at the site of the explosion. ( AP: Chinatopix )

Windows in buildings as far as six kilometres away were blown out by the force of the blast, which caused a magnitude-2.2 seismic shock.

A woman, who only gave her surname, Zhi, said she lived about five kilometres from the plant and that glass from windows smashed by the force of the blast injured her neighbours.

"At the time of the explosion, I was almost deafened and I was terribly frightened," she said.

Schools were closed and nearly 1,000 residents were moved to safety as a precaution against leaks and additional explosions, the city government said.

An aerial photo shows the fires that firefighters battled for hours to bring under control. ( AP: Ji Chunpeng, Xinhua )

The blast created a crater, and more than 900 firefighters were deployed to extinguish the fire that burned into the night.

The cause of the blast was under investigation, and people responsible for operations at the plant had been placed "under control", Xinhua said.

It was not clear whether anyone had been formally arrested.

Drains and waterways running through and from the plant complex have been blocked to prevent toxic chemicals from running into the nearby Yellow Sea, under orders from the Ministry of Ecology and Environment.

More than 600 people were injured, 90 of them seriously. ( AP: Chinatopix )

Company's dismal track record

The disaster occurred at a factory run by the Jiangsu Tianjiayi Chemical Company.

Located among a cluster of chemical factories in Yancheng, it has a dismal safety record.

In February 2018, China's State Administration for Work Safety cited 13 types of safety hazards at the company, including mishandling of tanks of toxic benzene, believed to be the source of Thursday's explosion.

Other local media reports said chemical fertiliser may have also been involved in the explosion.

An aerial view of damaged buildings owned by the company, which had more than a dozen safety violations. ( AP: Ji Chunpeng, Xinhua )

The plant had racked up 1.79 million yuan ($376,000) in fines since 2016 for violations of environmental regulations, according to judgments issued by local environmental protection bureaus.

The infringements included improperly dealing with hazardous waste and evading air pollution supervision.

A 2017 explosion that killed 10 at a nearby plant prompted the State Administration of Work Safety to dispatch inspectors.

They discovered over 200 safety hazards at chemical factories in Yancheng and four nearby cities, including 13 at the Tianjiayi plant.

Safety hazards cited included leaks and drips, employees who didn't understand safety procedures, and a lack of emergency shut-off valves on tanks carrying flammable chemicals.

It took many hours for firefighters to put out the massive blaze. ( Reuters )

In 2014, the company's chairman Zhang Qinyue, and its former supply chief Wu Guozhong were arrested on suspicion of dumping and burying hazardous waste by-products near a temple and a village landfill, according to a Jiangsu court criminal judgment.

They were convicted in 2017 and the company was fined 1 million yuan ($210,000).

AP/Reuters