A powerful and shallow earthquake of magnitude 7.9 struck off the west coast of the Indonesian island of Sumatra on Wednesday, the US Geological Survey said.
The epicentre was 808 km (502 miles) southwest of Padang, USGS said. It was 10 km (six miles) deep.
There were no immediate reports of damage or casualties but the shallower a quake, the more likely it is to cause damage. USGS originally put the magnitude at 8.2, and then 8.1, before lowering it to 7.9.
A local hospital in Padang, a coastal city on the Indonesian island of Sumatra, temporarily evacuated its patients after the earthquake.
Footage showed a crowd of people gathered outside the hospital, some standing, while others sat by a fence. One elderly man was holding what appeared to be a drip.
Indonesia issued a tsunami warning for West Sumatra, North Sumatra and Aceh following the quake.
Indonesian and Australian authorities called off their tsunami alerts within two hours of the 7.9 magnitude tremor, though it was still unclear if the quake had destroyed any buildings or killed people in Sumatra.
The National Disaster Mitigation Agency said a tsunami was unlikely.
Any rescue operation will be hampered by the dark, which falls early in the tropical archipelago.
Indonesia, badly hit by the Indian Ocean tsunami in 2004, straddles the so-called "Pacific Ring of Fire", a highly seismically active zone where different plates on the earth's crust meet and create a large number of earthquakes and volcanoes.
A 9.15-magnitude quake opened a fault line deep beneath the ocean on December 26, 2004, triggering a wave as high as 17.4 meters (57 feet) that crashed ashore in more than a dozen countries to wipe some communities off the map in seconds.
The disaster killed 126,741 people in Aceh alone.