The quake struck at 9:09 pm (1409 GMT) at a depth of 30 kilometresmiles) under the sea with an epicentre 53 kilometres southwest of the town of Sinabang, off the coast of Northern Sumatra.

It was also felt in the towns of Medan, the provincial capital, and Sibolga and on the island of Nias.

"We do not expect any damage or casualties and our colleagues in Northern Sumatra have said they do not expect any damage or casualties," agency offical Agus told AFP.

A local journalist in Medan told AFP the tremor was felt "very briefly" and said there was no panic among residents.

A 9.3-magnitude quake off the west coast of Aceh on the northern tip of Sumatra island triggered the December 26 tsunamis that left at least 217,000 people dead around the Indian Ocean, including 131,000 in Aceh alone.

Indonesia sits on the so-called Pacific Rim of Fire, where the meeting of continental plates causes high volcanic and seismic activity.

Indonesia earlier this week activated the initial phase of a tsunami early warning system off the coast of Sumatra aimed at avoiding a repeat of last December's tsunami.

Two sets of moored surface buoys and ocean-bottom pressure sensors were activated off western Sumatra on Tuesday by Indonesian and German scientists.

The instruments, the first two sets of a total of 15 to be installed along the coast of the vast archipelago, could also be uplinked to a satellite and information transmitted to a monitoring station near the town of Padang in West Sumatra province, Indonesian officials said.

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