Two powerful offshore earthquakes struck the same region in the southern Philippines hours apart on Friday with the first 7.4 magnitude temblor killing at least seven people, setting off landslides and prompting evacuations of coastal areas nearby because of a brief tsunami scare.

The second one had a preliminary 6.8 magnitude and also sparked a local tsunami warning by authorities.

It was caused by movement in the same fault line, the Philippine Trench, at a depth of 37 kilometers (23 miles) off Manay town in Davao Oriental province, Philippine Institute of Seismology and Volcanology chief Teresito Bacolcol said.

"This (the second one) is not an aftershock, this is a distinct event which we call doublet," Bacolcol told The Associated Press.

Bacolcol and other authorities expressed fears that the second nighttime earthquake could further weaken or collapse structures already undermined by the first one.

President Ferdinand Marcos Jr., facing his latest natural disaster after a recent deadly quake and back-to-back storms, said the potential damage was being assessed and rescue teams and relief operations were being prepared and would be deployed when it was safe to do so.