A strong earthquake measuring 6.8 struck off the coast of the island of Mindanao in the Philippines on Saturday, the country's seismology agency said, and the Pacific Tsunami Warning Center said there was a risk of large waves as far away as Indonesia,.

The Philippines Institute of volcanology and seismology said the earthquake was about 57 km southwest of Sarangani. It was felt in most parts of Mindanao, the biggest island in the south of the archipelago nation.

There were no initial reports of damage or casualties.

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.