An earthquake with a magnitude of 7.3 struck off the west coast of Indonesia's Northern Sumatra on Wednesday, the US Geological Survey reported.
A tsunami warning has been issued by the Pacific Tsunami Warning Center.
The quake, which had a depth of 29 kilometres, hit at 2:37 am (1837 GMT) around 261 miles southwest of Banda Aceh.
An official at Indonesia's Meteorology and Geophysics Agency said it also had put out a tsunami alert, but that there were no immediate reports of casualties.
"The quake was in the sea and a tsunami warning is in force, but so far we have no reports of casualties or damage," Suharjono, the agency's technical chief, told the media.