There have been 15 aftershocks since a four-point-nine-magnitude earthquake struck waters southwest from Jeju Island's Seogwipo region late afternoon on Tuesday.

The Korea Meteorological Administration(KMA) said no serious damage has been reported from the biggest quake to hit the southernmost island or its secondary shocks, the last of which hit at 3:06 p.m. Wednesday.

Acting Jeju Governor Koo Man-seop called for efforts to reinforce the island province, saying Jeju is no longer safe from the dangers of an earthquake.

The acting governor also urged provincial authorities to continue monitoring for additional shocks and disaster management.

The latest quake is the eleventh strongest in magnitude to hit on or off South Korea. The strongest to date was a five-point-eight magnitude quake that struck the southeastern city of Gyeongju in September 2016.