Foxconn Technology Group has vowed to investigate the hiring of underage interns at its plant in Yantai, Shandong province.

The company has confirmed that vocational school students between the ages of 14 and 16 had worked at the factory for three weeks.

"An internal investigation carried out by our company found that some participants in a short-term student internship program administered at our base in Yantai are under the legal working age of 16," the company said in a statement.