Fauzi, an official with the local geological agency who goes by only one name, put the magnitude at 7.7. He did not have any immediate reports of damage or injuries.
The Pacific Tsunami Warning Center said the quake had the potential to generate a destructive tsunami along coasts within 600 miles of the epicenter.
Indonesia is prone to seismic upheaval due to its location on the so-called Pacific "Ring of Fire," an arc of volcanos and fault lines encircling the Pacific Basin.
In December 2004, a massive earthquake off Indonesia's Sumatra island triggered a tsunami that battered much of the Indian Ocean coastline and killed more than 230,000 people — 131,000 of them in Indonesia's Aceh province alone.
A tsunami off Java island last year killed nearly 5,000.