A statement on a Web site affiliated with the publicity department in Sichuan province, where the Chengdu factory is located, said a conflict between Foxconn workers and a restaurant owner had set off the riot, China Daily reported.
Foxconn's factory in Chengdu supplies parts for Apple's iPhone and iPad.
The Hong Kong newspaper Ming Pao reported about 1,000 workers of the Taiwan company were involved in the riot and said many were injured and more than 10 were arrested.
The newspaper said the riot was triggered by workers' dissatisfaction with wages and the company's management of dormitory rooms.
The Sichuan Web site statement said seven workers from the Foxconn factory had dinner in a restaurant near the employees' dormitory and, under the influence of alcohol, damaged the restaurant with wine bottles. China Daily said the statement said the workers believed a quarrel between the restaurant owner and his wife "had ruined their dining mood."
The statement said the restaurant owner had a conflict with the workers, a customer called police and the workers began running back to their dorm, shouting, "They are beating us."
The statement said about 100 workers in Foxconn's dorm threw objects including bottles of mineral water down stairs, starting the riot.
The provincial government statement said four workers were held overnight and no one was injured.