A major earthquake of 7.8 magnitude struck off the coast of Aceh on the Indonesian island of Sumatra on Wednesday, but there were no immediate reports of a tsunami or casualties.

A Reuters photographer on Simeulue island, south of Aceh, said there was panic and electricity was cut off after the quake. Metro TV reported that people rushed to higher ground in some areas.

The quake was centred 204 km (127 miles) west-northwest of the coastal town of Sibolga and was at a depth of 46 km (28.6 miles), the U.S. Geological Survey said. It had initially reported the quake's magnitude at 7.6.

The Reuters witness said there were at least threee aftershocks.

The Pacific Tsunami Warning Center said there was no threat of a destructive widespread tsunami. However, it added: "There is the possibility of a local tsunami that could affect coasts" no more than 100 km (62 miles) from the epicentre of the quake.

In December 2004, a magnitude 9.15 quake off the coast of Sumatra's Aceh province triggered an Indian Ocean tsunami that killed about 226,000 people in Indonesia, Sri Lanka, India, Thailand and nine other countries.