The cause of the explosion was under investigation, the official Xinhua News Agency said early Tuesday.
Authorities initially said 17 were killed in the blast in the underground garage at a hospital for employees of the Xuangang Coal and Electricity Co. Ltd. in Shanxi province. But Xinhua said the toll rose to 27 hours later and might rise as rescue efforts continue.
Most of the victims were hospital staff and their family members, Li Jianzhang, an official with Xuangang, was cited as saying by Xinhua late Monday.
Li said the company had "no idea how many people were still missing." The report did not give any more details on where the bodies had been found.
A two-story residence directly above the garage was destroyed, said Li You, a hospital official.
Another nearby five-story residence several feet away, which houses hospital staff, was damaged with many of the windows blown out, the hospital official said.