Jakarta - At least four people were killed, nearly 60 others wounded and more than 1,500 buildings were damaged after a powerful undersea earthquake struck off the Indonesia's North Sulawesi early Monday, officials said.

The 7.7-magnitude quake struck at 1:02 am (1702 GMT Sunday) with its epicenter in the sea about 138 kilometres north-west of Gorontalo on North Sulawesi, about 1,950 kilometres north-east of Jakarta. It occurred about 10 kilometres beneath the seabed.

The US Geological Survey measured the quake at 7.5 on the Richter scale.

Indonesia's National Meteorology and Geophysics Agency (BMG) briefly issued a tsunami warning, but the alert was canceled after no tidal waves materialized, an official said.

A series of aftershocks followed the powerful quake, with the strongest measuring 6.0 on the Richter scale, sparking a further panic among residents and preventing them from returning to their homes.

Authorities said thousands of residents in Gorontalo, Palu and other regions remained outdoors hours after the quake. They were staying in the hills for fear of possible tidal waves despite the lifting of the official tsunami warning.

"The residents had fled to available hills around their houses since the first earthquake happened," the state-run Antara news agency quoted Risan Dewanto, the coordinator of disaster management in northern Gorontalo district, as saying.

"At least four people were killed and 59 others injured after being hit by falling debris," said Rustam Pakaya, head of the Health Ministry's crisis centre.

Pakaya explained at least two men and one woman were killed and 27 others injured in the Buol district of central Sulawesi province, while an elderly man died and 32 others were wounded by falling debris in northern Gorontalo district.

Central Selawesi provincial spokesman Fed Abbas said in a telephone interview that at least 1,500 homes collapsed or were damaged by the quake.

The official Antara news agency reported more than 20,000 residents fled their homes in Buol and nearby areas.

Hotel guests and residents in Gorontalo city also abandoned buildings and fled to higher ground to escape possible tidal waves.

Indonesia, the world's largest archipelago, sits on the Pacific "Ring of Fire," the edge of a tectonic plate prone to seismic upheaval.

The country launched a new high-technology system early last week aimed at detecting potential tsunami and providing faster alerts in a region battered by frequent earthquakes.

A major earthquake and subsequent tsunami struck in December 2004, leaving more than 170,000 people dead or missing in Indonesia's Aceh province and around 500,000 homeless. (dpa)