Another aftershock of 6.2 degree on Richter scale hit southern Philippines Saturday where a 6.9-magnitude earthquake and two strong aftershocks of 7.3 and 7.7 occurred earlier in the day, the U.S. Geological Survey reported.

The quake, with a depth of 563.9 km, hit south southwest of Cotabato, Mindanao, where three major jolts occurred at 6:08 a.m., 6:51 a.m. and 7:15 a.m. in succession, the Philippine Institute of Volcanology and Seismology (Phivolcs) said.

So far, there were no reports of casualties or damage and no tsunami warning was issued.

Telecommunication lines in some areas in the southern Philippines were cut out following the three strong earthquakes.

Philippine Long Distance Telecommunication Company's services were temporarily cut out in the southern city of General Santos and nearby areas.

Phivolcs chief Renato Solidum said that the first earthquake, which was tectonic in origin, had a magnitude of 6.9.

Asked why the USGS's measurements were much higher than that of Phivolcs, Solidum explained that the two agencies use different types of measuring earthquake magnitudes.

The quakes were felt in the cities of Zamboanga, Pagadian, Koronadal and General Santos.

A resident, named Yolly Andrias, in the southern city of Cotabato, said they were still sleeping when the strong quake awoke them. In other areas, vehicles alarm systems went on.

"We have received no reports of damage or casualties," said Marlon Macapili, a fire official of the Autonomous Region in Muslim Mindanao.

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

The worst earthquake in the country happened on Aug. 16, 1976, after a tsunami caused by a quake killed between 5,000 and 8,000 people in the Moro Gulf region in southern Philippines.