Police arrested Lin Binwei, 26, Xinhua reported, after the fire that broke out early Saturday morning.
Among the deceased were two children and migrant workers, Xinhua reported.
The building housed three homes, which were rented out for office use and living quarters for two shopkeepers of an online store that sold women's shoes, Xinhua said.
Police said Lin admitted to having a personal conflict with one of the shopkeepers, Liu, who survived the fire.
Investigators said video records show Lin's car near the scene of the fire.