A reactor at one of South Korea's largest nuclear plants shut down Wednesday, officials said, at a time of creeping public anxiety over safety in the country's nuclear industry.

The reactor, one of six at the Yeonggwang complex in the southwest of the country, shut down at 2:44pm (0544 GMT), a spokesman for the Korea Hydro and Power Co. told AFP.

"The cause of the stoppage is as yet unknown and investigations are underway. We don't know when it will resume operations," the spokesman said.

He stressed there was no sign of any radiation leak.

South Korea has 23 reactors which are meant to meet more than 30 percent of electricity needs. But the sector is currently undergoing a crisis of confidence following a series of shutdowns and a scandal involving parts provided with fake safety certificates

Wednesday's incident brings to seven the total number of reactors currently offline.

State prosecutors have launched an extensive probe into the safety certificate fraud, which forced the shutdown of two reactors in May and delayed the scheduled start of operations at two more.

Last year, officials said eight suppliers were found to have faked warranties covering thousands of items used in a number of reactors.

The scandal further undermined public confidence already shaken by the 2011 Fukushima nuclear disaster in Japan and its ongoing repercussions.

Despite the concern, the government has vowed to push ahead with its nuclear power programme and plans to build an additional 16 reactors by 2030.