In pictures: Asia commemorates the 2004 tsunami

Indonesia's Aceh province, which was closest to the earthquake, was the first to be hit by the tsunami shortly after the magnitude 9 quake struck on December 26, 2004. The northwest coast of Sumatra saw waves as high as 30 meters (100 feet) move up to 3.2 kilometers (2 miles) inland. More than 170,000 people died in Indonesia alone. Only larger and sturdier buildings, like this mosque, survived.

Fifteen years on, thousands of people gathered close to mass graves for the victims in Banda Aceh to pray and leave flowers. Flags were set at half mask throughout the province and nearby, fishers canceled sea trips in their boats as a mark of respect to the dead. The bodies of many of the victims have never been found but years later, some remains continue to be discovered.

More than 8,000 people, including many tourists, were killed when the tsunami slammed into Thailand's southwestern coast. The region is a popular destination for many foreign and local tourists during Christmas. Beach resorts in Phang Nga, Phuket and the Phi Phi islands were some of the hardest-hit areas. Years after the disaster, the bodies of almost 400 victims remain unidentified and unclaimed.

On Thursday, hundreds attended a tsunami memorial ceremony at Ban Nam Khem, a small fishing village that lost about half of its population of 5,000 when the waves rolled in. Tourists and locals attended the service at the Ban Nam Khem Tsunami Memorial Park, where they viewed a photo display of victims and laid flowers.

Sri Lanka witnessed a death toll of 30,000 from the tsunami including more than 1,500 people who had crowded into this train from Colombo to the southern port city of Galle. Already overcrowded when the first wave struck, many nearby locals seeking sanctuary climbed on top of the carriages, only for the train to flipped off the tracks by subsequent walls of water.

Fifteen years on, hundreds of people boarded a train in Sri Lanka's capital to take the same journey. The train to Galle stopped close to the exact location near Peraliya where the original train was overturned and dragged several meters. Several people brought flowers to lay at the tracks. Nearby is the Tsunami Memorial Buddha statue at Peraliya which has become a regular place of remembrance.

In India, over 12,400 people lost their lives when the devastating tsunami hit. The town of Nagapattinam (pictured above) was one of the worst-hit coastal areas in the southern Indian province of Tamil Nadu.

Thousands of people gathered at memorials in India on the anniversary of the disaster. People scattered flower petals in the Bay of Bengal and observed a minute of silence at the time the tsunami struck the coast fifteen years ago.