A tsunami watch declared after two major earthquakes off the coast of Indonesia's Aceh province has now been partly lifted, the Pacific Tsunami Warning Center (PWTC) says.
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.
Alerts remain in place for Indonesia, India and the islands.
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 (USGS), which documents quakes worldwide, said the first Aceh quake was centred at a depth of 33km (20 miles), about 495km from Banda Aceh, the provincial capital.
The BBC's Karishma Vaswani in Jakarta says there were reports of the ground shaking for up to five minutes.
The earthquake was initially reported as 8.9 magnitude but was later revised down to 8.6 by the USGS. Quake officials said a tsunami had been generated and was heading for the coast of Aceh.
A PTWC alert said that sea level readings indicated a tsunami was generated and that it "may already have been destructive along some coasts," without specifying where.
A Thai disaster official said a 10cm wave had been recorded on Koh Miang island, off Phang Nga.
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".