South Korean Yonhap News Agency reported a 5.4 magnitude quake which struck close to the city of Pohang on the southeastern coastline around 2:29 pm local time.
No reports have emerged so far about casualties or damage.
Mark Zastrow, who lives in Seoul, tweeted: "Woah, quake in Pohang and just felt it in Seoul, a few seconds after I got the alert on my phone".More news: 25 injured by collision between two trains at Singapore's Joo Koon station
The seismic intensity was the second biggest in the country's history after the biggest ever quake of 5.8-magnitude hit the Gyeongju city, just south of the Pohang city, in September past year. As of 3:00 p.m. local time, four minor injuries were reported, according to the firefighting agency.
The quake's epicentre was about 6km north of the southeastern port city of Pohang, Yonhap news agency reported.
Before the main tremor, earthquakes of 2.2 and 2.6 magnitude struck areas near Pohang city. Electric lamp hanging from the ceiling was shaken, with books falling from a bookshelf.More news: Manchester United can Sign €80m Star for €45m in January - Mou's Priority
Tremors were felt in the South Korean capital Seoul, around 270km from Pohang, Yonhap added.
Korea Hydro & Nuclear Power (KHNP) 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. Nuclear power plants in Gyeongju and the surrounding areas are reported to be safe and unaffected by the quake. As the government is working to rescue residents in the affected areas, President Moon Jae-in, who came back from his 8-day tour of Southeast Asia this afternoon, just finished holding an emergency meeting on the situation with his top aides.More news: India Summit: Modi calls for efforts to uproot terrorism
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