In southern Thailand, where half the 5,300 dead were holidaymakers, people recounted stories of horror and miraculous survival as the churning debris-laden waters swept in without warning, obliterating resorts and villages.

As dusk loomed, hundreds gathered for a candlelit memorial on Khao Lak, much of which was washed away by towering waves.

Swiss national, Katia Paulo, 45, lost her boyfriend on a nearby beach. "I had my back to the ocean," she said. "My boyfriend called me ... the only thing I remember is his face.

"I knew I had to run, then the wave caught me. I was pushed under water many times and thought it was the end."

She held tight to a tree branch and found herself six metres of the ground as the waters receded.

Nearby, Thai Somjai Somboon, 40, said she still grieved for the loss of her two sons, who were ripped from their home when the waves smashed into their fishing village, Ban Nam Khem. "I remember them every day," she said, with tears in her eyes.

The official ceremony, led by the Thai premier, was due to be held at police patrol boat 813, swept about 2km inland, which is now a memorial to the disaster.

The world poured money and expertise into the relief and reconstruction, with more than US$13.5 billion collected in the months after the disaster.

Almost US$7 billion in aid helped to rebuild more than 140,000 houses in Indonesia's Aceh province, where most of the nation's 170,000 victims died.

The main city, Banda Aceh, staged the nation's official remembrance at a seven-hectare park, near the epicentre of the undersea quake, which bore the brunt of 35-metre-high waves. "Thousands of corpses were sprawled in this field," Indonesian Vice-President Jusuf Kalla told the crowd - many among them weeping.

In Sri Lanka, where 31,000 people were killed, survivors and relatives of about 1,000 victims who died when waves derailed a passenger train, boarded the restored Ocean Queen Express and headed to Peraliya - the exact spot where it was ripped from the tracks, 90km south of Colombo.