MANILA: A powerful earthquake that killed at least 61 people in the Philippines this week raised the seabed by as much as two meters, exposing coral and harming marine life, the environment department said Sunday.

The 7.8-magnitude tremor in southern Mindanao island on Monday has also left at least 40 people missing, according to updated tolls from the disaster agency.

Local residents first reported the geological phenomenon known as "coastal uplift" two days after the quake, which extended the shoreline by as much as 200 meters in some places, the environment department said.

A shifting of the Cotabato Trench "pushed upward part of the coastlines of Sarangani and Davao Occidental (provinces)... exposing the bottom of the sea that was originally submerged", the Philippine Institute of Volcanology and Seismology said in a statement.

"Approximately 2m [meters] was the mapped uplift."

The Cotabato Trench, which lies as close as 50 kilometres off the coast of southern Mindanao, is the site of frequent seismic activity, including a "swarm" of thousands of mostly small earthquakes recorded in January.

A team dispatched to the area "found that long stretches of shoreline, coral reef and seagrass beds have been exposed", the environment department said.

An official who spoke to AFP on Sunday said they could not yet say precisely how wide an area had been affected given the size of the area they needed to survey.

Images released by the department's regional office showed a large swathe of exposed coral with dead fish and other aquatic life lying on top.

Residents initially reported the changes to the seabed out of concern that they might be poisoned by the fumes from decaying sea life.

"These exposed corals and seagrass beds had begun dying off alongside their resident organisms such as reef fishes, eels, clams, and shells," the environment department said.

seismic activity

Deadly Philippine quake raised seabed by up to two meters