South Korea's third-strongest earthquake since 1978 shook the Taean area in the western part of the country on Tuesday, but there were no immediate reports of serious damage.
The magnitude 5.1 earthquake, centered about 100 km northwest of West Gyeongnyeolbi Archipelago off Taean, happened at around 4:48 a.m., according to the Daejeon Meteorological Office.
The temblor shook homes and other structures in Taean and Seosan, with its aftershocks felt even in Seoul, Incheon and its adjacent areas.
"I was woken up because my bed was severely jolted. I was afraid," a resident in Incheon told Yonhap News Agency, requesting not to be named.
"We expect no serious damage from the quake because it took place in the offing," said Lee Ji-min, a researcher at the Korea Meteorological Administration. "Most reports that we have so far received are about tremors of buildings."
It was the third-strongest earthquake to hit the Korean Peninsula since seismic monitoring began in 1978.
The strongest were two magnitude-5.2 earthquakes that hit areas near Mount Songni on Sept. 16, 1978, and in waters about 80 kilometers east of Uljin, North Gyeongsang Province, on May 29, 2004.
The temblor in Ulsan rattled buildings in the Gyeongsang provincial area and was felt throughout the country.
When unofficial records are included, a magnitude 5.3 quake that hit Uiju in North Korea's North Pyongan Province in 1978 was the strongest. (Yonhap)