The magnitude 5.4 quake hit north of Pohang, located 370 kilometers southeast of Seoul, at around 2:29 p.m., the state weather agency said.
Korea Hydro & Nuclear Power said the six nuclear reactors in Gyeongju, about 45 kilometers south of the epicenter, as well as other reactors on the southeastern coast are all functioning normally.
"All reactors, including those in Gyeongju, are operating normally without power shutdown or decreased power output," the KHNP said in a statement. "Although there is no breakdown in facilities or radiation leakage, we will conduct an in-depth inspection and release the result later."
Following the earthquake, Paik Un-gyu, minister of trade, industry and energy, convened an emergency meeting via conference call to check major energy facilities, including power plants, pipelines and petroleum reserves, and ordered energy firm chiefs to take necessary measures if needed.
"The ministry will team up with utilities companies and related organizations to monitor major energy facilities to prepare for any contingencies," the ministry said in a release.
Nuclear reactors in the region operated normally when the nation's strongest-ever earthquake at magnitude 5.8 hit Gyeongju in September 2016. At the time tremors were felt as far as Seoul.
Among 24 reactors in the nation, 18 are located along the southeastern coast, which is more exposed to tremors, as recent earthquakes in nearby Japan could have destabilized the fault lines on the Korean Peninsula.
Following the 2011 Fukushima nuclear meltdown, South Korea has been upgrading the nuclear reactors' seismic safety features to withstand a magnitude 7.0 quake
For Shin Kori units 5 and 6 under construction in the southeastern city of Ulsan, the KHNP said they will be built to be safe against a magnitude 7.4 quake. (Yonhap)