A 7.9 magnitude earthquake has struck off the coast of western Indonesia, the US Geological Survey (USGS) reports.
There have been no immediate reports of damage.
The USGS said the earthquake struck at 19:49 local time (12:49 GMT). It said the epicentre was 808km (502 miles) southwest of the city of Padang, and 10km deep.
Indonesian officials issued a tsunami warning for the regions of West Sumatra, North Sumatra and Aceh.
The shallow quake, which hit southwest of the island of Sumatra on Wednesday, had a depth of 10 kilometers (six miles).
The epicenter was located 808 kilometers (502 miles) southwest of Padang.
The USGS originally categorized the quake as a magnitude 8.2, and later an 8.1, before lowering it to a 7.9.
Indonesia has issued a tsunami warning for West Sumatra, North Sumatra, and Aceh, according to the National Meteorological Agency.
In 2004, a 9.1 magnitude earthquake struck 160 kilometers (99 miles) off the western coast of northern Sumatra, resulting in a tsunami. A total of 230,000 people were killed across a dozen countries, including Thailand.
Indonesia straddles the so-called 'Pacific Ring of Fire,' a highly seismically active zone where neighboring tectonic plates violently clash, resulting in a large number of earthquakes and volcanoes.
