Many others remained buried under the rubble of the toppled building in Jiangsu Province, local police officials said.
The condition of three persons, of the nine injured, was stated to be serious, state-run Xinhua news agency reported.
Several people are still believed to be buried under the rubble of the three-story building, the report said.
The explosion occurred this morning in the city of Suzhou, an industrial hub in the Yangtze River Delta.
A preliminary investigation showed that the blast was caused by a gas leak, the report said.