More than 600 people have died in Haiti after floodwaters raged through the island in the wake of tropical storm Jeanne, UN officials say.
About 80% of Gonaives has been affected
Aid agencies counted some 500 bodies in the northern coastal city of Gonaives alone, a spokesman for the UN peacekeeping mission in Haiti said.
And the toll is climbing considerably, a Red Cross spokesman told the BBC.
Two days of steady rain have washed away entire houses - sometimes reaching up to the third floor.
But the emergency relief operations have just begun, and access is difficult and limited, the head of International Federation of the Red Cross, Hans Havik, said.
The storm earlier reportedly killed 11 people in the neighbouring Dominican Republic, and has since moved north into the Atlantic.
Mr Havik said the casualties were so high in Haiti because of widespread deforestation in the impoverished island.
In Gonaives - the biggest city in the area - an estimated 80% out of a population of more than 200,000 has been affected, UN's World Food Programme said in a statement.
Poorest country in Western Hemisphere
80% live below absolute poverty threshold
Severe or moderate stunting affects 47% of under fives
*Data from UN World Food Programme
At least 56 people have died in the town of Port-de-Paix, 18 in Chansolme, 14 in Gros-Morne, nine in Pilate and eight in Ennery, officials said.
It was not clear if any lives were lost in the island of La Tortue - which was barely visible under the water, according to UN officials.
But Dieufort Deslorges, a spokesman for Haiti's civil protection agency, said the government had been in contact with officials on La Tortue and "nothing happened there".
Haiti's interim Prime Minister Gerard Latortue has called for international help, describing the flooded area as "a vast sea".
He has declared three days of national mourning.
People were left huddled on rooftops, while roads around the city of Gonaives were transformed into rivers.
Many others were reported missing and injured in the country, prone to floods due to massive deforestation. Hospital workers there say medical supplies are also urgently needed.
"I lost my kids and there's nothing I can do," Jesner Estimable, whose daughter was killed and another of whose five children was missing, was quoted as saying by the Associated Press news agency.
"All I have is complete despair and the clothes I'm wearing," Mr Estimable said.
UN peacekeepers are helping the relief effort, as are international aid agencies.
The UN World Food Programme says it has sent its first convoy of 12 trucks carrying 40 metric tons of emergency food aid to the city of Gonaives.
But Mr Havik said access was proving difficult - especially as the UN force in Haiti had few helicopters.
In May, a storm killed about 3,000 people on the country's border with the Dominican Republic.
NORTHERN HAITI UNDER WATER
1. The island of La Tortue was barely visible but Haitian official now say nothing happened there.
2.About 30% of Port-de-Paix city is reported to be covered by water along the coast and nearby plantations are reported to be under water. The road to Gonaives is flooded.
3. The water level of the river is reported to be very high and some villages on its banks have been flooded.
4. Flooding has hit all urban areas of Gonaives, affecting about 80% of the population - some 500 people are believed to have died there.