MANILA, Oct. 10 (Xinhua) -- An offshore earthquake with a preliminary magnitude of 6.9 struck Davao Oriental province in the southern Philippines on Friday night, the Philippine Institute of Volcanology and Seismology said.

In a report, the institute said that the quake, which occurred at 7:12 p.m. local time, struck at a depth of 10 km, approximately 36 km southeast of the municipality of Manay.

The institute said that the tectonic quake will trigger aftershocks and cause significant damage.

Based on the local tsunami scenario database, it is expected to experience wave heights of more than 1 meter above the normal tides and may be higher on enclosed bays and straits, the agency said, warning that "these waves may continue for hours."

This is the second strong earthquake that has hit the same area on the same day. A magnitude 7.4 earthquake struck off the coast of Manay on Friday morning.

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