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.

"This is not only a violation of China's Labor Law, it is also a violation of Foxconn policy and immediate steps have been taken to return the interns in question to educational institutions."

The statement added that Foxconn will work with the educational institutions to fully investigate "how this happened and the actions that must be taken to ensure that it can never happen again".

The company admitted it is responsible for the violations and said it has apologized to each of the students who were involved in the case. It also pledged to fire any employees who were found to be responsible for the violations.

Louis Woo, spokesman for Foxconn, said the company immediately began an investigation into the matter last week after learning of the underage employees from an NGO, which he declined to name. The allegations were eventually substantiated, prompting the company on Monday to send home all of the students under the age of 16 who had been working at the factory.

He did not say how many students were involved in the case, nor which vocational schools they came from.

Foxconn, based in Taiwan, employs nearly 70,000 workers at its factory in Yantai.

"We are really sorry and we apologize to the students for causing this inconvenience," Woo said, adding that all of the company's factories have been ordered to look into whether they employ workers or interns who are younger than 16.

He said the interns at Foxconn cannot be forced to work, can quit any time they want and are not allowed to work night shifts or overtime.

"Interns are paid the same salaries as ordinary workers at Foxconn, so there is no reason we would take these risks (of hiring underage interns)," he said.

Foxconn has a short-term internship program with various vocational schools and other educational institutions on the mainland. The internship programs last from three to six months.

A student at Yantai Engineering and Technology College, who asked to remain anonymous, told China National Radio that he had once worked night shifts at the Yantai plant's circulation department. He said the schedule was difficult.

The factory eventually "fired" him after he took leave three times without first receiving permission, and a teacher at the college told him he would also be expelled from the school for failing to finish an internship, China National Radio reported.

More than 50 students at the college under the age of 16 were employed in the factory in September. The report said some of them worked seven days a week.

The college disagreed with those claims on Wednesday.

"Nearly 95 percent, or even 98 percent, of the students who participated in the internship program we had with Foxconn were older than 16," a publicity officer at the college who only identified herself as Zhong told China Daily on Wednesday.

"The college has been organizing such internship programs with enterprises such as Foxconn because we are a vocational training institution. Government regulations and the nature of the college oblige us to carry out these ‘internship educations' to fulfill our responsibilities.

"Without such programs, our students will be unable to practice what they learn in classes and to know what real manufacturing processes and techniques are."

Zhong said no student has been expelled because they failed to complete an internship, adding that the college has not made money from the programs.

"We have no vested interest in these programs or the enterprises we cooperate with," she said. "Foxconn pays the students during their internship but not the college."

"Normally vocational schools will not make money by sending students to factories through an internship," said a teacher at the Beijing Polytechnic College who only gave her name as Zhou. "My college will send teachers to businesses where our students work as interns, thus making sure they are treated fairly."

However, Duan Yi, a lawyer at Guangdong Laowei Law Firm, said underage labor is too common in China.

"We've dealt with cases in which schools made profit by establishing partnerships with factories and sending students to work there."

Contact the writers at huangyuli@chinadaily.com.cn and zhaolei@chinadaily.com.cn