Indonesia and Thailand are marking 20 years since a tsunami caused the death of hundreds of thousands of people in one of the worst natural disasters in modern history.

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 saw an estimated 230,000 people killed across a dozen countries.

The tsunami was triggered by a 9.1-magnitude earthquake that struck off the west coast of North Sumatra, Indonesia, at 7.59am local time on 26 December 2004.

Indonesia was the country with highest number of deaths, but India, Sri Lanka and Thailand were also badly hit.

Many wept openly at the mass grave in Ulee Lheue village, where more than 14,000 unidentified and unclaimed tsunami victims are buried. It is one of several mass graves in Banda Aceh, the capital of Indonesia’s northernmost province.

Footage showed people visiting a mass grave in Siron to remember the victims of an event that shocked the world.

In Thailand, people gathered in Phang Nga province to honour the victims and those affected.

To mark the 20th anniversary of the disaster, Sky News has spoken to people who survived the tsunami, one of whom lost his brother to the huge waves while they holidayed together in Thailand.

In Aceh, the tsunami reached 167ft (51m) high, according to the United Nations Office for Disaster Risk Reduction (UNDRR) and caused flooding up to three miles (5km) inland.

The infrastructure in Aceh has been rebuilt and is now more resilient than 20 years ago.

Early warning systems have been installed in coastal areas to alert residents of potential tsunamis, providing crucial time to seek safety.

The rebuilding efforts were made possible by the support of international donors and organisations, who contributed significant funds to help the region recover.

Schools, hospitals, and essential infrastructure that were destroyed by the disaster have been reconstructed with enhanced strength and durability, ensuring better preparedness for future challenges.

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Various communities in Aceh commemorate the tsunami yearly along with the government and local authorities.

In Banda Aceh, art communities in early December spread disaster awareness through theatrical or musical performances that can be easier for people to follow and target all groups, including those born after the tsunami.