A huge explosion rocked a gas plant in central China on Friday, killing at least two people and injuring another 18, state media said.

Another twelve people were missing after the blast, said state broadcaster CCTV, which shattered windows and doors of buildings in a three-kilometre (1.9-mile) radius.

Official news agency Xinhua had earlier said "many people" were injured by the explosion, which happened at 5:50 pm local time.

Xinhua said the blast occurred in the air separation unit of the Henan Coal Gas Group factory and not in the gas tank areas, citing a source in the Yima city government. All production at the plant has been stopped.

"Many windows and doors within a three-kilometre radius were shattered, and some interior doors were also blown out by the blast," CCTV said on its Twitter-like Weibo social media account.

Local media showed amateur videos of a massive column of black smoke billowing from the factory and debris littering the roads.

Other images showed the doors and windows of homes blown out and shuttered shops with dented metal fronts.

A bloodied man was seen being helped out of a van in a video posted on social media.

AFP could not immediately verify the authenticity of the footage. Deadly industrial accidents are common in China, where safety regulations are often poorly enforced.

In March, a blast at a chemical plant in eastern Jiangsu province killed 78 people and injured hundreds.

The powerful explosion in the eastern city of Yancheng toppled several buildings in the industrial park, blew out windows of nearby homes and even dented metal garage doors.