In Indonesia’s province of Aceh – the worst hit area – Vice-President Jusuf Kalla led tributes to the dead at the Siron mass grave.
Memorial ceremonies will also take place in Thailand and Sri Lanka.
More than 200,000 people died when an underwater earthquake set off massive waves on December 26, 2004.
In Aceh’s capital, Banda Aceh, Jusuf Kalla thanked local volunteers and the outside world for helping Aceh recover from the tragedy. He also presented awards to ambassadors from the donor nations.
Earlier, thousands of people earlier gathered at the city’s Great Mosque – a 19th Century building that was one of the few structures in the town to survive the tsunami.
The mosque’s imam, Asman Ismail, said the tsunami had taught a “valuable lesson” to Aceh, which had been the scene of an armed conflict for nearly 30 years.
“After the tsunami, no-one fights against each other, people live in harmony and peace till this day,” he said.
Efforts to end the conflict resumed after the tsunami, culminating in a peace deal between the government and the rebels in August 2005.
In Thailand, people are marking the anniversary with a series of solemn events and religious rites throughout the day.
In the small fishing village of Ban Nam Khem, Phang Nga province, people have been laying flowers at a memorial wall displaying names of the victims.
The village was devastated by the massive waves.
Nearly 5,500 people died in Thailand, half of whom were foreign tourists.
In Sri Lanka, the Ocean Queen Express train – which has become a symbol of the tragedy for the nation – is at the centre of commemorative events.
The overcrowded train was hit by the tsunami south of the capital Colombo. More than 1,700 people died, in what was the world’s biggest rail disaster.
Survivors and relatives of those who died boarded the restored train carriage and headed to Peraliya, where the train was struck.
Sweden, which lost over 500 of its citizens in the disaster, will hold a memorial service in the Uppsala Cathedral on December 26.
The strength of the quake off Indonesia’s coast – the biggest tremor in the world since 1964 – unleashed giant waves that rushed across the Indian Ocean.
The tsunami also hit Bangladesh, Myanmar, Malaysia, the Maldives and later reached the east African nations’ of Kenya, Somalia and Tanzania.
Tsunami warning systems and emergency procedures have been implemented since the disaster to try to minimize casualties in the future.
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