People have started gathering in prayer and are visiting mass graves in Indonesia’s Aceh province to mark 20 years since the massive Indian Ocean tsunami, one of modern history’s worst natural disaste

A powerful 9.1-magnitude earthquake off the coast of the Indonesian island of Sumatra on Dec. 26, 2004, triggered a tsunami that killed around 230,000 people across a dozen countries, reaching as far as East Africa. Some 1.7 million people were displaced, mostly in the four worst-affected countries: Indonesia, Sri Lanka, India and Thailand.

Survivors and victims' relatives will next week mark the 20th anniversary of the 2004 Indian Ocean earthquake and tsunami, which killed more than 220,000 people across more than a dozen countries.At the time of the earthquake,