Mourners in Sri Lanka buried their dead with bare hands Tuesday as rescuers rushed to check isolated pockets of Indonesia for survivors of explosive tidal waves that the United Nations said may be history's costliest natural disaster. Nearly 40,000 people were dead, and officials expected toll to rise further. Eleven nations in the densely populated band of destruction spanning as far as Africa tallied corpses as they filled tropical beaches and choked hospital morgues. The International Red Cross feared malaria and cholera would add to the toll as aid agencies mounted what U.N. officials said would be the world's biggest relief effort. "This is unprecedented," said Yvette Stevens, an emergency relief coordinator of the U.N. Office for the Coordination of Humanitarian Affairs. Almost a third of the dead were children. Thousands of people were missing, and millions homeless. More than 18,700 people died in Sri Lanka, about 15,000 in Indonesia, more than 4,000 in India and more than 1,000 in Thailand, with numbers expected to rise. The Indonesian vice president's estimate that his country's coastlines held up to 25,000 victims brought the potential toll up to 50,000.