A nuclear reactor in South Korea's southeastern region shut itself down after its reactor operation system gave a warning signal, the state-run plant operator said Thursday.

The Reactor-1 in Uljin Nuclear Power Plant, automatically stopped operating its nuclear reactor and turbine generator as of 6:41 p.m., according to the Korea Hydro & Nuclear Power Co.

It froze itself on the warning signal and the shutdown falls under a "zero" rating according to International Atomic Energy Agency (IAEA) standards, it said.

The state-run operator said the halt of the reactor will not have any impact on the plant's safety, adding it is unrelated to a radiation leak.

The operator immediately reported the shutdown to related government agencies to find out the reasons for the freeze.

The Uljin generator is a pressurized water reactor with a capacity of 950,000 kilowatts, and has been operating since 1988. (Yonhap News)