Two powerful offshore earthquakes have struck the same region in the southern Philippines, with the first 7.4 magnitude tremor killing at least seven people.

The first quake also set off landslides and prompted evacuations of coastal areas nearby because of a brief tsunami scare.

A second quake with a 6.8 magnitude on Friday also sparked a local tsunami warning.

Both were caused by movement in the same fault line, the Philippine Trench, Philippine Institute of Seismology and Volcanology chief Teresito Bacolcol said.

"The second one is a separate earthquake, which we call a doublet quake," Bacolcol told The Associated Press.

"Both happened in the same area but have different strengths and epicentres."

Bacolcol and other authorities expressed fears that the second nighttime earthquake

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