A 6.8-magnitude earthquake struck off the Philippines Saturday, the U.S. Geological Survey said, but there were no immediate reports of casualties or damage.

It struck at a depth of 41 kilometres (25 miles) in Mindanao, more than 700 kilometres southeast of the capital Manila, the USGS said.

The Pacific Tsunami Warning Center advised that hazardous tsunami waves were possible off the coasts of the Philippines and Indonesia.

Hazardous waves could spread 300km (190 miles) away from the epicentre, which was in the sea south of the city of General Santos, the Center added.

The Philippines lies on the so-called Ring of Fire, a vast Pacific Ocean region where many of Earth's earthquakes and volcanic eruptions occur.