Most buildings on the Somali island of Hafun were swept away by the deadly Indian Ocean tsunami, an emergency aid relief team has revealed.
Beaches along East Africa were buffeted by huge waves
Roads washed away by the sea are hampering the delivery of food aid to some 4,500 islanders affected.
Waves which swept 7,000km (4,000 miles) from the epicentre left a trail of smashed buildings and boats along the East African coast.
More than 130 people in East Africa are known to have died in the floods.
"Almost 95% of Hafun's buildings have been destroyed," the UN World Food Programme's Ali Issay - part of the first relief team to reach victims of the tsunami - told the BBC's Focus on Africa programme.
Dazed inhabitants have moved to higher ground and are wandering about asking for help, as there is no food and no fresh water on the island, he said.
"We have nothing," destitute people told him.
Hafun's governor asked for emergency assistance and told aid agencies that he feared up to 8,000 people across the island could be affected by the flooding.
Twelve Hafun residents have been confirmed dead and many more are missing. Bodies can still be seen floating in the sea, the governor told Mr Issay.
More than 30 tons of food aid is expected to arrive on Wednesday on the island off the north coast of Somalia by a bridge accessible during low tide, the WFP says.
Meanwhile, the UN is planning an aerial assessment of Somalia's coastline on Thursday, where thousands of other people are reported to have lost their homes.
Speaking on Kenyan television on Tuesday night, Somali Prime Minister Ali Mohammed Ghedi said he feared the disaster would cause an outbreak of cholera.
He and other members of the government - which is currently based in neighbouring Kenya as Mogadishu is considered too dangerous for ministers - are due to visit the most affected regions of northern Somalia on Saturday.
Countries along the East African coast are still trying to assess the total loss of life and damage caused by the tsunami.
Ten people drowned in Tanzania and more than 1,000 people have been made homeless in Madagascar.
Three people died in the Seychelles, where a bridge linking the main airport and capital, Victoria, was destroyed while a village in northern Mauritius was submerged for almost three hours following the surges.
In Kenya, beaches that were closed on Sunday reopened, amid government warnings to tourists to take precautions.
About 15 fishing boats were damaged in the French territory of Reunion.
The British government warned its citizens in Madagascar, Mauritius, the Seychelles, Kenya and Tanzania to be alert for potential danger from the sea surges.