An Indian Ocean tsunami alert is in place after two huge quakes off the coast of Indonesia's Aceh province.
A quake with a magnitude of 8.6 triggered the initial warning, which was renewed after another quake a few hours later measuring 8.3 on the Richter scale.
The Pacific Tsunami Warning Center has advised national authorities across the Indian Ocean region to "take appropriate action".
But there have been no immediate reports of damage or casualties.
The region is regularly hit by earthquakes.
The Indian Ocean tsunami of 2004 killed 170,000 people in Aceh alone and some 250,000 around the region.
The US Geological Survey, which documents quakes worldwide, said the first Aceh quake was centred at a depth of 33km, about 495km from Banda Aceh, the provincial capital.
Indonesian President Susilo Bambang Yudhoyono had told reporters in the capital, Jakarta, that there had been no tsunami reports so far, "but we remain vigilant".
Tremors were felt as far away as Singapore, Thailand, Sri Lanka, Malaysia, Bangladesh and India.