The explosion in Kunshan, a city in the eastern province of Jiangsu near Shanghai, "has resulted in 65 deaths", state broadcaster China Central Television (CCTV) said in an internet post.
The explosion occurred Saturday morning at a workshop in a metals factory, state media said. The cause of the incident has not yet been identified.
More than 100 people were injured when a "powerful blast ripped through" the factory, China's official Xinhua news agency said.
Graphic photographs posted online showed a charred body being wheeled on a stretcher, and people with burned clothing sitting on the ground outside a factory complex that was billowing black smoke.
"The scene is a mess, it's unrecognisable," a witness at the scene wrote on Sina Weibo, a Chinese equivalent of Twitter.
Industrial accidents occur with some regularity in China, where safety standards are often lax. A fire at a poultry plant in the northeast of the country killed 119 people last year.
The People's Daily newspaper reported online that the factory in Kunshan employs 450 staff. State media said the blast occurred at a wheel hub polishing workshop inside the factory.
Medical staff have been sent from China's commercial hub Shanghai to treat burns victims, the People's Daily added in an online post.
Jiangsu province is located on China's coast. Many local and foreign companies have facilities there producing goods for export.