A siren rings out as Indonesian survivors and relatives of victims begin commemorations for more than 220,000 people who died two decades ago when a tsunami devastated coastal areas around the Indian Ocean, in one of the worst natural disasters in human history. In Indonesia's Banda Aceh city, an official ceremony at the Baiturrahman Grand Mosque kicked off a series of memorials across Asia with a three-minute-long siren at the exact time a major earthquake caused giant waves on December 26, 2004. IMAGES