The residents of 18 countries bordering the Indian Ocean are participating in drills being conducted to test a warning system set up following the deadly 2004 tsunami.
Wednesday's drill is intended to simulate a tsunami similar to the one sparked by the 9.2-magnitude quake off Indonesia in 2004, the United Nations said in a statement. That quake generated waves that eradicated entire coastal communities, killing some 230,000 people in one of the worst natural disasters of modern times.
The object of the exercise was to allow Indian Ocean countries and Australia to test their communications, review their emergency procedures and identify any weaknesses, the UN Educational, Scientific and Cultural Organization said.
Countries participating included Australia, Bangladesh, India, Indonesia, Kenya, Madagascar, Malaysia, Maldives, Mauritius, Mozambique, Burma, Oman, Pakistan, Seychelles, Singapore, Sri Lanka, Tanzania and East Timor.
The scenario was meant to replicate events that may occur if another 9.2- magnitude quake strikes the region.
Test earthquake warnings were issued and messages were transmitted to countries and then to towns and villages.
The simulated tsunami spread across the entire Indian Ocean over a 12-hour period beginning with an epicentre off the coast of Indonesia and with wave effects reaching South Africa.
"When the siren sounded, I immediately thought of my child, grabbed her and ran," said Bakhtiar, 50, who lives in the village of Gampong Pie, along the Indonesian coastline in Aceh province.
In Aceh's Ulee Lheue village, which was all but wiped out by the tsunami, about 200 residents gathered at a mosque after an explosion sounded from loudspeakers meant to signal an earthquake.
Around 10 minutes later, a siren blared out, starting the drill.
"We want to send the message to the world that we continue to improve our disaster mitigation skills," said Aceh Vice-Governor Muhammad Nazar.
Dubbed Exercise Indian Ocean Wave 09, the drill was the first comprehensive test and evaluation of the warning system put in place after the 2004 disaster, said UNESCO.
Some survivors from the 2004 tsunami refused to participate because the memories of the day were too paralyzing to go through the drill, according to reports.
The drill came two weeks after a tsunami smashed into the Pacific islands of Samoa, American Samoa and Tonga, killing at least 183 people.
In Thailand, where more than 5,000 Thais and foreign tourists perished, no evacuation drill was planned, but its National Disaster Warning Centre was responding to the dummy telegrams, faxes and emails being sent out by the Hawaii-based Pacific Tsunami Warning Center, said Capt. Saran Thappasook.
In Burma, also known as Myanmar, officials were to relay the warnings to tsunami-prone areas, said Thein Tun, director general of the Meteorological Department, while in Malaysia 1,200 villagers on the northern resort island of Langkawi were directed to higher ground as firefighting trucks and ambulances ferried the elderly and pregnant women.
Medical teams searched areas for survivors and people with mock bandages were carried on stretchers while others pretended to be dead.
Heavy equipment, speedboats and aircraft were also used in the drill to simulate search and rescue operations, warnings and aid efforts.
People have become much more aware of how to react when a tsunami warning is issued since 2004, said Puthukudiyiruppu resident Sanmuaja Palmweu.
"Before 2004, we knew nothing about tsunamis, but thanks to all the drills and training we know what to do now, and how to pass the information if something is coming," Palmweu told Reuters.
There were reports that some of the tsunami warning towers had failed to emit a siren during the drill. But most officials cited the drill as a success.
"We believe that all or most of the countries in the Indian Ocean are a lot better prepared now than they were in 2004," said Ray Canterford, an official at Australia's Bureau of Meteorology.
Despite the success of the drill, some experts maintain the early-warning system is not effective because the time interval between alarms sounding and the giant wave slamming into the coast can be very short, especially in countries like Indonesia, which is close to fault lines.