The explosion occurred late on Saturday in Kaili city in Guizhou province, Xinhua said, citing local police. It was caused by illegally stored chemicals in an adjacent room.
"The explosion and ensuing fire totally obliterated the cafe," Xinhua said, adding that the blast also shattered the windows of nearby residential buildings.
Police have detained a man for the illegal possession of the chemicals and have taken the cafe's boss and manager into custody for questioning, it added.
(Reporting by Sui-Lee Wee, Editing by Daniel Magnowski)