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 disasters.

Survivors and victims’ relatives will this 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.

People gathered in prayer and visited mass graves in Indonesia's Aceh province to commemorate 20 years since the Indian Ocean tsunami.

On Dec. 26, 2004, a 9.1 magnitude earthquake struck off the west coast of Sumatra, causing a massive wave that devastated Asian coastal communities across thousands of miles.

Tearful mourners prayed Thursday as ceremonies began across Asia to remember the 220,000 people who died two decades ago when a tsunami hit coastlines around the Indian Ocean, in one