Indonesian authorities have lifted the tsunami warning that was issued after huge earthquake hit northern Sulawesi island.
The quake had a magnitude of 7.5 and was at a depth of 21 km, with its epicentre 136 km northwest of the provincial capital of Gorontalo, the US Geological Survey said.
Two further weaker aftershocks struck in the same area of the Celebes Sea bordering the southern Philippines.
Indonesia's meteorological agency issued a tsunami warning after the first quake, but lifted it within a few hours.
There were no immediate reports of casualties.
Indonesia launched a new hi-tech system this week aimed at detecting a potential tsunami and providing faster alerts in a region battered by frequent earthquakes, though experts say large parts of the country are still not covered and the system will not be fully operational until 2010.
The sprawling archipelago of some 17,000 islands was hit by a devastating tsunami four years ago that left an estimated 170,000 people dead or missing in Aceh province.