MANILA: Three major quakes measuring between magnitude 7.3 and 7.4 hit the southern Philippines early Saturday, seismologists said, but there were no reports of damage and no tsunami warning was issued.

The underwater quakes struck at a depth of between 575 and 605 kilometres (350 and 375 miles), just over 100 kilometres southwest of Cotabato, in Mindanao, said the US Geological Survey.

The Hawaii-based Pacific Tsunami Warning Center said no destructive tsunami was generated by the quakes, the first of which hit at 6:08 am (2208 GMT Friday).

"It was kind of mild," said Monisa Tulawie, a staff member at the Cotabato city mayor`s office, who told AFP she felt one of the quakes.

Other residents contacted by phone were unaware of what had happened, saying they had not been woken by the tremors.

"We have received no reports of damage or casualties," said local fire official Marlon Macapili of the Autonomous Region in Muslim Mindanao, a self-ruled area that includes four provinces around Cotabato.

Seismologist Wilmer Legaspi of the Philippine Institute of Volcanology and Seismology said the quakes were too deep to cause substantial surface damage, although flimsy structures could be vulnerable.

"It can cause damage to buildings made of light materials," he told AFP.

The Philippines is an archipelago of more than 7,000 islands with many people living in communities close to the sea.

The country sits on the Pacific Ring of Fire, where continental plates meet, causing frequent seismic and volcanic activity.

BDST: 1019 HRS, July 24, 2010