A tsunami warning has been issued in the Indian Ocean after powerful earthquakes off the coast of Indonesia's Aceh province, prompting evacuations from coastal regions and alarm in areas struck by a devastating wave in 2004.
A small tsunami measuring 10cm reached Thailand's Andaman Coast, an official said.
"A 10-centimetre tsunami wave generated by the first earthquake hit Koh Miang off Phang Nga," the director of Thailand's National Disaster Warning Centre, Somsak Khaosuwan, said on Thai television.
A tsunami measuring 17cm had been generated and was headed for the Aceh province, Victor Sardina, a geophysicist at the Hawaii-based Pacific Tsunami Warning Center, said.
He said the total vertical measurement of the wave, according to monitoring gauges, was 35cm, making the height 17cm. He did not provide a time estimate for landfall.
"It doesn't look like a major tsunami," Sardina said. "But we are still monitoring as tsunamis come in waves."
Phillip Charlesworth, head of the International Federation of Red Cross and Red Crescent Societies delegation in the Indonesian capital Jakarta, told Al Jazeera that the quake lasted for about three minutes.
"The shaking was quite violent, from conversations with our staff," he said. "There appears to be no apparent damage. We certainly don’t know what the humanitarian impact is as yet. There are no reports of any tsunamis coming ashore, although local authorities are taking precaution of evacuating coastal communities."
There were several strong aftershocks, including one at a 8.2 magnitude and the depth of 10km.
"The aftershock continued for four minutes, and it was strong," correspondents in Banda Aceh, the provincial capital, said. "People are panicking and running outside their home and from buildings."
The tremors were also felt in Bangkok, where buildings swayed, but there were no reports of damage.
The initial quake had struck at a depth of 33km, 495km from Banda Aceh.
The tsunami watch was in effect across the whole Indian Ocean, including Australia, Pakistan, India, Somalia, Madagascar, and many other countries. A tsunami watch means there is the potential for a tsunami, not that one is imminent.
"Earthquakes of this size have the potential to generate a widespread destructive tsunami that can affect coastlines across the entire Indian Ocean basin," the US Pacific Tsunami Warning Center said.
People in Banda Aceh jumped into cars and the backs of motorcycles, clogging streets as they fled to high ground. Eye witnesses said people panicked across the island of 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 out of buildings and there is really a lot of panic there.
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.
In Sri Lanka, residents on the coast were ordered to move inland to avoid being hit by any large waves.
A government statement said waves could hit the island's eastern port district of Trincomalee.
"There is a strong possibility of a tsunami hitting the island after the earthquake in Indonesia," meteorological department deputy director M D Dayananda said.
He said the quake in Indonesia was felt in Sri Lanka, which is 1,340km northwest from the location of the quake.
People near the coast in six Thai provinces were ordered to move to higher places and stay as far away as possible from the sea. The Phuket airport, right on the coastline, was closed.
Indonesia straddles a series of fault lines that makes the vast island nation prone to volcanic and seismic activity. A 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.