MANILA -- An offshore earthquake with a preliminary magnitude of 6.4 rocked Davao Occidental province in the southern Philippines on Wednesday night, the Philippine Institute of Volcanology and Seismology said.

The institute said the quake, which occurred at 7:21 pm local time (1121 GMT), hit at a depth of 139 km, about 66 km southeast of Sarangani Island.

The institute said the tectonic quake will trigger aftershocks but will not cause damage.

The archipelagic Philippines has frequent seismic activities due to its location along the Pacific "Ring of Fire."