CCTV showed footage shot by residents of large plumes of thick, black smoke rising from the plant. Several firefighting trucks were shown in the factory compound. News websites posted photos showing survivors or those who were killed being lifted onto the back of large trucks, their bodies black, presumably from burns or soot.
Some survivors were seen sitting on wooden cargo platforms on the road outside the factory or being carried into ambulances, their clothes apparently burned off and their skin exposed.
The explosion occurred at 7:37 a.m. at a workshop in the factory, which polishes wheel hubs. Rescuers pulled out 44 bodies at the site, while 24 other people died at a hospital, officials said. At least 187 people were injured.
More than 120 of the injured were sent to hospitals in Kunshan and the nearby city of Suzhou. Burn experts from a Shanghai hospital arrived in Kunshan to help, the official Xinhua News Agency reported.
A preliminary investigation showed that the blast was likely a dust explosion, Xinhua said.
The factory is operated by the Kunshan Zhongrong Metal Products Company, which according to its website was set up in 1998 and has a registered capital of $8.8 million. Its core business is electroplating aluminum alloy wheel hubs, and it supplies GM and other companies, the website said.
In a statement, GM confirmed that Zhongrong is part of its network of suppliers. "We can confirm Zhongrong is a supplier to GM's global supplier Dicastal," the statement said.
Police took away five senior Zhongrong executives to assist in the investigation, officials said, without providing details.
A woman who answered the main phone line at the Zhongrong metal company said it is a Taiwanese enterprise. She refused to give her name, any other information or the contact numbers of company staffers handling the case.
Calls to the city's government and police rang unanswered.
A dust explosion is caused by the fast combustion of particles suspended in air in an enclosed space. The particles could include dust or powdered metals such as aluminum. They would have to come into contact with a spark, such as fire, an overheated surface or electrical discharge from machinery.
Workplace safety is a major problem in China, where safety regulations are often ignored and enforcement can be lax. In June 2013, 119 workers were killed when a fire raced through a chicken processing room at a poultry plant in the northern province of Jilin. The fire appeared to have been sparked by an explosion caused by leaking ammonia, officials said.
Sixty-two people were killed and scores injured in the eastern port city of Qingdao in November when a pipeline exploded. Investigators said the blast was caused by sparks from a jackhammer being used to repair a manhole cover following an oil leak.
Associated Press researcher Henry Hou contributed to this report.