A South Korean nuclear reactor shut down Friday after a technical malfunction, operators said, at a time when the government is already warning of serious power shortages because multiple reactors are offline.

The state-run Korea Hydro and Nuclear Power (KHNP) said an investigation was underway to confirm the precise cause but added there was no immediate safety threat.

The incident occurred at the Hanwool Nuclear Power Plant in Uljin County on South Korea's eastern coast.

At proper capacity, South Korea's nuclear reactors supply more than 35 percent of the country's electricity needs.

But nine of 23 reactors are currently offline for multiple reasons, including a scandal involving parts provided with fake safety certificates.

State prosecutors have launched an extensive probe into the 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.

South Korea's nuclear sector has been dogged by a series of malfunctions, forced shutdowns and corruption scandals that have undermined public confidence already shaken by the 2011 Fukushima nuclear disaster in Japan.

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