An 8.7-magnitude earthquake has struck off the coast of Indonesia, sending residents around the region dashing out of their homes and offices in fear.
The Pacific Tsunami Warning Centre said a tsunami watch was in effect for the entire Indian Ocean and individual countries including Thailand, Indonesia, Sri Lanka and India issued tsunami warnings.
Many areas in those nations were devastated by the Boxing Day tsunami in 2004 which killed more than 200,000 people.
The US Geological Survey (USGS) says the quake, which was felt as far away as the Thai capital Bangkok and southern India, was detected 33 kilometres beneath the ocean floor about 495 kilometres south-west of Banda Aceh.
A 6.5 aftershock has already been recorded but Indonesia's president says there are no reports of casualties or damage in Aceh.
Thai officials issued evacuation orders in the tourist hotspots of Phuket and Phangnga, as well as other coastal provinces.
"We warn people in every district to evacuate immediately because there is a possibility of a tsunami," a local disaster official told Reuters.
The Indian National Centre for Ocean Information Service issued a red high-level warning for the Andaman and Nicobar islands, and also put out lower alerts for the coasts of Andhra Pradesh and Tamil Nadu states.
Sri Lankan and Malaysian officials have asked residents on the coast to move inland to avoid being hit by any large waves.
The Bureau of Meteorology says no tsunami warning has been issued for the Australian mainland.
People have taken to ABC Online's Facebook page in the wake of the earthquake to express their concern.
"I am in Padang, west Sumatra. We are fine, many people rush from their home to higher place[s]. Please pray for us," Andri Rusta wrote.
"Friends in Medan [north Sumatra province] have felt it quite badly - just regrouping and assessing now," Leanne Sibthorpe posted.
Violent shaking
Indonesia's disaster management agency said power was down in Aceh province and people were gathering on high ground as sirens warned of the danger.
Residents in Aceh reported the ground shaking violently.
"It began as a mild tremor and then got stronger," an AFP correspondent said, adding that the ground shook for about five minutes.
"There are people trying to evacuate, some are praying and children at a school were panicking as teachers tried to get them out," he said.
Elsewhere, electricity is down, there are traffic jams leading to higher ground, while sirens and Koran recitals are being sounded across the area.
The 8.7 quake was in roughly in the same area as a December 26, 2004, quake of 9.1 magnitude, which sent huge tsunami waves crashing into Sumatra, where 170,000 people were killed, and across the Indian Ocean.
In all, the 2004 tsunami killed about 230,000 people in 13 Indian Ocean countries, including Thailand, Sri Lanka and India.
The 2004 quake was at a depth of 30km along a fault line running under the Indian Ocean, off western Indonesia and up into the Bay of Bengal.
