An natural disaster measuring 5.4 on the Richter scale jolted South Korea on Wednesday.
The quake was centred off the coast about 9.3 kilometres (5.8 miles) northwest of the port city of Pohang, according to the U.S. Geological Survey.
Tremors were felt across the nation including Seoul and Busan, with some residents in the affected areas reporting damage.
Further details are awaited.
The most powerful quake recorded in the south was a 5.8-magnitude tremor that hit the southeastern city of Gyeongju in September a year ago. No casualties have been reported yet.
South Korea has relatively little seismic activity, compared with Japan to the east. The Korea Meteorological Administration said that no injuries or major damages were immediately reported.
Photos and video footage sent to local TV stations showed crumbled street walls and furniture violently shaking inside people's homes and people rushing out of buildings in panic.
Its strongest quake on record was magnitude 5.8 in September previous year.