South Korea's Samsung Electronics has refuted fresh allegations by a labour protection watchdog that one of its suppliers in China hired child workers.

New York-based China Labor Watch (CLW) claimed in a report Thursday that Samsung supplier HEG Technology had hired people under the age of 16 at its facility in Huizhou, China.

The report said the factory, where components for Lenovo are also built, had hired new workers, and neglected to check their identification.

The youngest worker was found to be 14, the report said, adding the factory had also hired 117 college students, many of whom averaged 12.5 hours of work each day.

The student workers eventually quit their jobs, but complained that the factory owed them money, according to the report.

Samsung, however, insisted that a recent onsite investigation found no underage or student workers at the facility.

"The investigation found that there were no child workers nor student workers working in the Samsung Electronics production line at HEG," the company said in a statement e-mailed to AFP on Friday.

The world's largest mobile phone maker said it had called for a joint investigation with the labour group to verify the results before its report was issued.

"We find it regrettable that CLW issued the allegations ... without any mention of our statement," it said.

Samsung stressed again that it has a zero tolerance policy regarding child labour, and actively works with its Chinese suppliers to screen out underage hires.

"We deeply care about the health and safety of all our employees, and employees at our suppliers and strictly maintain a zero tolerance policy on child labour," the company said.

This is the second case where the rights monitoring group has accused HEG of hiring underage workers.

In 2012, the group claimed HEG had violated child labour regulations. Samsung rejected the claim but acknowledged "inadequate" practices including excessive overtime.

The labour group, however, said its latest investigation showed that "conditions at HEG failed to improve".

Samsung has more than 200 suppliers in China and there have been repeated allegation over working practices in recent years.

In July, Samsung temporarily suspended business with Dongguan Shinyang Electronics following criticism that its monitoring of illegal labour practices was ineffective.