The city of Changshu in Jiangsu province, about 80 kilometers northwest of Shanghai, said in a brief social media post that the fire broke out around 4.30am.
The cause remains under investigation.
It's not clear how many residents survived.
An earlier report by the official Xinhua News Agency said more than 20 people lived in the house, citing unnamed sources.
Telephones at the city's publicity department rang unanswered.