Jakarta - Indonesia briefly issued tsunami warning after a 7.7-magnitude undersea earthquake struck early Monday off the country's North Sulawesi province and nearby regions, triggering panic among residents. The tsunami alert was cancelled about an hour later, after no tidal waves materialized, seismologists said. There were no immediate reports of casualties or damage.
The National Meteorology and Geophysics Agency (BMG) said the quake measuring 7.7 on the Richter scale struck at about 01:02 am Monday (1702 GMT Sunday). The US Geology Survey put the quake at 7.5 on the Richter scale.
Its epicentre was at a depth of about 10 kilometres beneath the sea about 138 north-west of Gorontalo in North Sulawesi, BMG said in a short message.
An 6.0-magnitude aftershock followed about 30 minutes later at a depth of 30 kilometres beneath the seabed, the agency said.
"A tsunami warning was cancelled after no tidal wave took place following the quake," said BMG official Subagyo, who like many Indonesians goes only by one name.
There were no immediate reports of injury and structural damage as a result of the latest in a series of quakes to rattle the vast archipelago nation, in recent weeks.
Media reports said the quake had caused widespread panic.
The state-run Antara news agency reported that thousands of residents in Gorontalo, Palu and Toli-toli districts ran out of their homes in panic.
Hotel guests and residents in Gorontalo city also abandoned buildings and fled to higher ground to escape possible tidal waves.
Many remained outdoors on hills in area after the warning was called off.
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 hi-tech system early last week aimed at detecting potential tsunamis 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.
