A strong earthquake of 6.9 magnitude struck off the southern Philippine island of Mindanao on Saturday and small tsunami waves were possible along its coast as well as in parts of Indonesia and Palau, the Pacific Tsunami Warning Center said.

There were no reports of casualties or damage, from the earthquake, which the US Geological Survey (USGS) said struck 193km east of the Philippine city of General Santos, at a depth of 60km.

The Pacific Tsunami Warning Center initially said "hazardous tsunami waves" were possible within 300km of the epicentre along the coasts of Indonesia and the Philippines.

The centre later said: "Tsunami waves are forecast to be less than 0.3m above the tide level for the coasts of Indonesia, Palau and the Philippines."

The USGS initially said the magnitude of the quake was 7.2 but later downgraded it to 6.9.

Residents of the southern Philippines said the earthquake lasted about a minute and some people rushed out of their homes but there had been no major damage.

"We've alerted the communities for a possible tsunami," Clinton Polancos, an official in the southern district of Governor Generoso, told Reuters.

"We're fine. The earthquake was not destructive." Indonesian media also said there were no reports of damage.

The Philippines and Indonesia are both on the Pacific "Ring of Fire", a horse-shoe shaped band of volcanoes and fault lines circling the edges of the Pacific Ocean.

Indonesia has been struck by two serious tsunami this year.

The first followed a 7.5 magnitude quake on the west coast of Sulawesi island in September. More than 2,000 people were killed.

The second tsunami struck a week ago, on Saturday evening, when part of a volcanic island collapsed in the Sunda Strait, between Java and Sumatra islands, generating tsunami waves that killed more than 400 people.

- Reuters