A magnitude 5.5 quake has struck off South Korea's southeastern coast, about 6km (4 miles) north of the southeastern port city of Pohang, Yonhap news agency reported.
The tremor occurred in an area 9 km north of the coastal city of Pohang in North Gyeongsang province at 2.29 p.m, according to the Korea Meteorological Administration.
The Korean peninsula rarely has to worry about significant quakes.
South Korea has relatively little seismic activity, unlike neighbouring Japan. No damage to them has been reported.
People evacuated buildings near the epicenter as soon as the felt tremors.
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There were no immediate reports of injuries.
South Korean President Moon Jae-In, on his way to Seoul after attending the Asean summit in Manila, is set to hold an emergency meeting upon arrival, his office said.
A cultural official checks Cheomseongdae, an astronomical observatory, in Gyeongju, some 370 kilometers southeast of Seoul, on September 20, 2016, one day after a magnitude 4.5 quake struck the ancient city with no immediate casualties or serious damage.
There are nuclear power plants and industrial facilities in the area.