The earthquake occurred at 8:55 pm (1355 GMT) and was centred 30 kilometres (18.6 miles) under the sea floor 92 kilometres southwest of Banda Aceh, the capital of Aceh province on Sumatra, according to the US Geological Survey.

There were no immediate reports of casualties.

The Indonesian archipelago sits on the Pacific Ring of Fire, where continental plates meet, causing frequent seismic and volcanic activity.

Indonesia was the nation worst hit by the earthquake-triggered Asian tsunami in December 2004, which killed some 168,000 people in Aceh province.

A 7.7-magnitude earthquake in July on the south coast of the main island of Java also killed more than 600 people.

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