The Pacific Tsunami Warning Center said hazardous waves could spread 300 km (190 miles) away from the epicentre.
But Renato Solidum, head of the Philippines seismology agency, told Reuters no tsunami warning was issued and there was no need to evacuate the areas affected.
But the agency had issued an advisory saying people could expect a minor drop in the sea level, large waves, and people should steer clear of the coast, he said.
The Philippines is on the geologically active Pacific Ring of Fire and experiences frequent earthquakes, several last month in the main island of Luzon, which were felt in the capital Manila.
Janet Bongolan, tourism officer at the Tuka Marine Park in Sarangani province, said people spilled out of their homes and into the streets during the earthquake, but most had returned and there was no sign of panic.
"There's no news here that there will be a tsunami. But we are watching out for aftershocks. We are careful here," she said by telephone.
"It was strong enough to awaken me and my family," he told a radio interview.
The US Geological Survey initially said the earthquake measured 7.2 but later downgraded it to 6.8.
(Reporting by Manuel Mogato, Neil Jerome Morales and Enrico dela Cruz; Writing by Martin Petty; Editing by Robert Birsel)
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