A series of powerful earthquakes have struck off Mindanao in the Philippines, but they did not generate a destructive tsunami, officials said.

The three quakes, with magnitudes of 7.3, 7.6 and 7.4, struck over the course of about 70 minutes starting at about 6:08 a.m. Saturday (12:08 p.m. Friday, Hawaii time.)

They were centered deep below Moro Gulf, roughly 65 to 75 miles west-southwest of Cotabato, Mindanao, and about 570 miles south-southeast of Manila, according to the U.S. Geological Survey.

The Pacific Tsunami Warning Center in Ewa Beach issued bulletins saying that no destructive tsunami was generated.

Gerard Fryer, geophysicist at the center, said the quakes were likely felt in the region but were centered at such a depth (about 400 miles) that they were unlikely to cause damage.

It is "very unusual to have such large earthquakes" so deep and in such quick succession, he said.

"They are clearly related but what it all means we don’t know," Fryer said, noting that scientists will be examining the event with great interest.

The quake were centered near Moro Gulf was centered at a depth of 375 miles, according to the USGS.