November 02, 2002 01:32 AM ET JAKARTA (Reuters) - An earthquake measuring 7.7 on the Richter scale struck off the northern coast of Sumatra island in Indonesia early on Saturday, but there were no immediate reports of damage.

"That's very big," said Mark Leonard, a seismologist at the Australian earthquake monitoring organization Geoscience Australia, adding the magnitude was similar to an earthquake that killed 20,000 people in the Indian state of Gujarat in 2001.

Geoscience Australia said the quake was centered under the Indian Ocean about 200 km (125 miles) southwest of the North Sumatran capital of Medan.

A resident in Medan, 1,450 km (900 miles) northwest of the Indonesian capital of Jakarta, said he felt the tremor for at least a minute and traffic was halted momentarily.

"Things were moving for at least one minute but there is no damage to houses here," the resident, who did not wish to be identified, said.

Leonard said the epicenter of the quake appeared to be about 60 km (40 miles) underground, which may have been too deep to produce a tsunami.

Officials from Indonesia's Meteorology and Geophysics office said the quake measured 5.5 on the Richter scale and that damage was likely even though early reports had not indicated this.

Undang Kaban, a Medan-based official for the meteorology office, said the impact of quake was felt most intensely in the coastal town of Tapaktuan in the south of Aceh province.

"The highest MMI (Modified Mercalli Intensity) reading was 5-6 and that was in Tapaktuan," Kaban told Reuters from Medan.

"Based on my experience, a reading of that magnitude would mean that damage is likely though we haven't heard any reports of damage yet," he said.

Officials in Tapaktuan, around 160 km from Medan, could not be immediately reached.

Kaban said the quake struck around 8.30 a.m. (0130 GMT).

The U.S. Geological Survey estimated the quake's depth at 33 km (20 miles).

-- Anonymous, November 02, 2002