The firm that makes Apple's iPhones suspended production at a factory in China after a brawl by up to 2,000 employees injured 40 people.
The cause of the fight in a dormitory was under investigation.
It erupted last night at a privately managed dormitory near a Foxconn Technology Group factory in the northern city of Taiyuan, the company and Chinese police said.
A police statement reported by the official Xinhua News Agency said 5,000 officers were dispatched to the scene.
The Taiwanese-owned company declined to say whether the factory was involved in iPhone production. It said the facility, which employs 79,000 people, would suspend work today and reopen tomorrow.
Foxconn makes iPhones and iPads for Apple and also assembles products for Microsoft and Hewlett-Packard. It is one of China's biggest employers, with some 1.2 million workers in factories in Taiyuan, the southern city of Shenzhen, in Chengdu in the west and in Zhengzhou in central China.
The violence did not appear to be work-related, the company and police said. Comments posted on Chinese Internet bulletin boards said it might have erupted after a security guard hit an employee.
The company has faced scrutiny over complaints in the past about wages and working hours. It raised minimum pay and promised in March to limit hours after an auditor hired by Apple found Foxconn employees regularly were required to work more than 60 hours a week.
