Friday's blast at the Henan Coal Gas Group factory left another 19 people seriously injured and more with light injuries said state broadcaster CCTV.
The blast shattered windows and doors of buildings in a three-kilometre (1.9-mile) radius.
It occurred in the air separation unit of Henan Coal's factory, CCTV said, with those hurt sent to four different hospitals. 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.
Authorities detained two dozen people in connection with the March 21 blast, which prompted the government to order a nationwide inspection of chemical firms.
A week after that explosion, seven died following a blast at an electronics component manufacturer in the same province.
In November, a gas leak at a plant in the northern Chinese city of Zhangjiakou, which will host the 2022 Winter Olympics, killed 24 people and injured 21 others.
Leaked chloroethylene came in contact with a fire source causing the explosion, authorities said in a February report, which also claimed the Chinese chemical firm responsible for the accident had concealed information and misled investigators.
In 2015, China suffered one of its worst industrial accidents when giant chemical blasts in the northern port city of Tianjin killed at least 165 people.
Friday's blast at the Henan Coal Gas Group factory left another 19 people seriously injured and more with light injuries, said state broadcaster CCTV.