A tsunami warning has been issued in the Indian Ocean after Indonesia's geophysical agency reported a powerful earthquake off Aceh province.
Wednesday's quake was measured at a preliminary 8.7-magnitude.
The geophysical agency said it had not received reports of damage from the Aceh quake or rise in water levels.
The US Geological Survey said it struck on a depth of 33km, 495km from Aceh's provincial capital, Banda Aceh.
A tsunami watch was issued across the whole Indian Ocean, including Australia, Pakistan, Somalia, Madagascar, and many other countries.
A tsunami watch means there is the potential for a tsunami, not that one is imminent.
The US Pacific Tsunami Warning Center said it was not yet certain a giant wave had been generated.
"Earthquakes of this size have the potential to generate a widespread destructive tsunami that can affect coastlines across the entire Indian Ocean basin," it said.
Residents fleeing
People in Banda Aceh jumped into cars and the backs of motorcycles, clogging streets as they fled to high ground.
Syarina Hasibuan in the Indonesian capital, Jakarta, told Al Jazeera that people panicked across Sumatra, running out of buildings and gathering in the streets.
"The earthquake was felt all the way to Padang, which is west Sumatra, and people ran down their buildings and there is really a lot of panic there.
“It will take about one hour until people from the meteorological agency can say if it is safe or not."
People on Twitter said tremors were felt in Singapore, Thailand, Malaysia and India. High-rise apartments and offices on Malaysia's west coast shook for at least a minute.
Thailand issued an evacuation order for its Andaman coast, a popular tourist destination. Thailand's National Disaster Warning Centre advised people in the area to move to higher places and stay as far away as possible from the sea.
Indonesia straddles a series of fault lines that makes the vast island nation prone to volcanic and seismic activity.
A giant 9.1-magnitude quake off the country on December 26, 2004, triggered a tsunami in the Indian Ocean that killed 230,000 people, nearly three quarter of them in Aceh.
PHOTO CAPTION
A seismologist points to a graphic showing an earthquake at a monitoring centre in Taipei.
Al-Jazeera