The tremour started in the sea 122 kilometres south-east of the town of Modayag at 0246 GMT at a depth of 20 kilometres, said The Straitstimes.
There are no reports yet of damage or casualties so far, but people reported feeling the quake, said the report. Pacific Tsunami Warning Center has issued an informational bulletin saying that based on all available data, a destructive Pacific-Wide tsunami is not expected.
Earthquakes are common in Indonesia, which lies on the Pacific "Ring of Fire" where continental plates collide, causing frequent seismic and volcanic activity. In 2004, a powerful earthquake off Sumatra island resulted in a tsunami that killed at least 230,000 people in countries including India.