Apple and its manufacturing partner Hon Hai Precision Co Ltd on Wednesday said that a small number of students were discovered working overtime in its Chinese factory, violating local labor laws.

The students worked voluntarily in the factory for more than 11 hours a day as part of a school internship program at a plant run by Hon Hai, also known as Foxconn.

"We discovered instances of student interns working overtime at a supplier facility in China. We've confirmed the students worked voluntarily, were compensated and provided benefits, but they should not have been allowed to work overtime," Apple said in a statement. The company added that it had sent staff to the site to address the violations.

"Our policies do not allow interns to work more than 40 hours per week on program-related assignments. Unfortunately, there have been a number of cases where portions of our campuses have not adhered to this policy," Foxconn said in a statement.

Labor rights groups have previously criticized Apple and Foxconn for excessive overtime, hiring underage workers and failing to provide health insurance.

Apple has been trying to get a grip of such issues, releasing annual reviews of the iPhone supply chain.