The ship was docked for repairs in the Beihai Shipbuilding Co. at the port of Qingdao, a major shipping hub on the northeastern Chinese coast.
A photo released by Xinhua news agency identified the ship as the Ocean Melody, which sails under a Liberian flag, according to the tracking website VesselFinder.
A total of 42 people had been on the vessel, and 12 of them were safely evacuated, Xinhua reported. Five were injured and taken to the hospital, and they remained in a stable condition.
The fire started around 11 a.m. Thursday and was extinguished by 2:30 p.m. local time.
China's President Xi Jinping issued "important instructions" to urgently conduct rescues of missing people on the ship, Xinhua said, adding that Premier Li Qiang called for "trapped" people to be rescued.