A major earthquake struck an area off northern Sulawesi in Indonesia early on Monday, causing a brief tsunami warning and triggering panic among residents.
The magnitude 7.5 quake was at a depth of 21km, with its epicentre 136km 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 later lifted it.
In the town of Poso in central Sulawesi, residents rushed out of their houses and patients were evacuated from a hospital.
Indonesia launched a new hi-tech system on Tuesday aimed at detecting a potential tsunami and providing faster alerts in a region battered by frequent earthquakes.
But 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, which lies in the seismically-active "Pacific Ring of Fire", was hit by a devastating tsunami four years ago that left an estimated 170,000 people dead or missing in Aceh province.
