MANILA—A strong 6.6 magnitude earthquake struck off Jolo Island at 10:39 p.m. Thursday, the Philippine Institute of Volcanology and Seismology said.

Three minutes later, a strong 6.3 magnitude aftershock followed.

There were no immediate reports of damage or injury.

The first tremor struck 281 kilometers southeast of Jolo at a depth of 515 kilometers.

It was felt at Intensity III in Davao City and Intensity II in General Santos City and Kidapawan City.

The Philippines sits on the Pacific “Ring of Fire” where continental plates collide causing frequent seismic and volcanic activity.