Residents of coastal towns and villages from Indonesia's Aceh province to Sri Lanka have taken part in a tsunami practice drill.
The exercise was a UN-backed initiative to test the warning systems and overall preparedness of nations in the region.
It was supposed to simulate the magnitude 9.15 quake that struck off Aceh on 26 December 2004 and triggered a huge tsunami.
About 230,000 people died in 2004 as the tsunami raced across the Indian Ocean and hit Indonesia, Thailand, Sri Lanka and India, including 170,000 deaths in Aceh alone.
In Aceh, several hundred took part in the simulation.
Officials from Indonesia's meteorology and geophysics agency in Jakarta issued the test earthquake warning, sending out the notification of a major quake off the coast of Aceh via a telephone text message, followed by a tsunami warning.
People with mock bandages were carried on stretchers, while others pretended to be dead.
Since the 2004 tsunami, early warning systems ranging from beach loudspeaker sirens to deep ocean monitor buoys have been set up at a cost of about $150m, according to an official.
A deputy governor in the Aceh province has declared today's drill a success, while warning against excessive reliance on technology.
UN officials are to issue an assessment within days.
A series of recent disasters in Asia has raised fresh questions over the state of preparations - including an earthquake on Indonesia's Sumatra island, and a series of tsunamis in Samoa and American Samoa.
Some experts have questioned the effectiveness of early alert systems, particularly if the time interval between the alarm and the tsunami hitting the area is very short, as would be the case in Indonesia, which lies on the fault lines.
Tsunami waves can travel at speeds of 800-1,000km/h.
The height of normal waves and tsunami waves is similar in deep ocean water, but closer to the shore, tsunami waves slow and swell, reaching heights of 10m or more.
Other countries participating included Australia, Bangladesh, India, Kenya, Madagascar, Malaysia, Maldives, Mauritius, Mozambique, Myanmar, Oman, Pakistan, Seychelles, Singapore, Tanzania and East Timor.
