The powerful 9.1-magnitude earthquake off the coast of the Indonesian island of Sumatra, triggered a tsunami that killed around 230,000 people across a dozen countries.

Christmas in 2004, a 9.1 magnitude earthquake under the Indian Ocean triggered tsunami waves that killed some 230,000 people across a dozen countries.

The earthquake and tsunami claimed the lives of over 200,000 people, the deadliest natural disaster of the 21st century.

Twenty years after the devastating earthquake and tsunami that claimed over 230,000 lives across the Indian Ocean region, thousands gathered in the capital of Indonesia's Aceh province on Thursday to commemorate the tragedy.

Survivors and families of victims visited mass graves, lit candles and comforted one another across Southeast and South Asia in ceremonies to mark the disaster that killed some 230,000 people.

Understanding of the Sumatran subduction zone and its hazards has increased since the 2004 Indian Ocean earthquake and tsunami.

People started gathering in prayer today and visiting mass graves in Aceh, one of the worst-hit areas by the Boxing Day Indian Ocean tsunami which killed an estimated 230,000 people across a dozen countries.