MANILA, Philippines -- (UPDATE 3) Two strong earthquakes shook the islands of Luzon on Saturday but there were no immediate reports of casualties or damage, government seismologists said.

The first quake, with a magnitude of 5.3, struck at about 11:05 a.m. (0305 GMT) and was followed a few minutes later by a stronger quake with a 6.5 magnitude, said Renato Solidum, director of the Philippine Institute of Volcanology and Seismology (Phivolcs).

"The quakes originated deep in the ground and when it reached the surface, it was not that strong," Solidum said in a radio interview.

There was no tsunami warning issued, he added.

The US Geological Survey recorded three aftershocks, the latest of which occurred at 2:40 p.m. (0640 GMT) with a magnitude of 4.9.

The tremors, tectonic in origin, were located 34 kilometers northwest of Mamburao, in Occidental Mindoro province at a depth of 81 kilometers, Solidum said.

The undersea quakes were felt in the capital Manila and surrounding areas where they set objects swaying.

Intensity 5 hit the island of Mindoro, intensity 4 in Manila, and intensity 3 in Quezon City and Batangas City, Solidum said.

They were also felt in Bataan and Pampanga, he said.

Solidum said the earthquakes were caused by the subduction of the South China Sea edge of the Eurasian Plate, which affected the Manila Trench.

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