Haiti's prime minister has warned of the threat of a serious outbreak of disease after devastating flooding caused by Tropical Storm Jeanne.
Aid trucks have struggled to make it through floodwaters
More than 700 people are now known to have died after Jeanne battered Haiti.
Aid agencies fear the toll will mount as 1,000 are missing and rotting bodies float in flooded urban areas.
"We have put out a call for help...Haiti cannot get out of a disaster like this alone," said Haiti's Prime Minister Gerard Latortue.
Speaking to France Info radio after visiting the stricken northern city of Gonaives, Mr Latorture said:
"We have a problem with bodies: there is a risk of epidemic. If you can picture
this: there is no electricity, the morgues are not working, there is water every where.
He also feared that, with large swathes of the north-west of the country still submerged, approaching Tropical Storm Carl could make things worse.
Days of torrential rain sparked mudslides, isolating communities as roads were destroyed and homes swept away by the water.
"The river destroyed my house completely and now we have nothing," 18-year-old Katya Silme told the Associated Press news agency, adding she and her family spent the night in a tree.
Residents forced to take shelter on rooftops in the northern port city of Gonaives reported bloated bodies floating along the streets.
A UN spokesman said the corpses had to be buried in mass graves as soon as possible, to try to stop disease spreading.
The UN World Food Programme (WFP) estimates 175,000 people are without food, water and electricity and in need of help.
UN peacekeeping troops - sent to restore order after President Jean-Bertrand Aristide was overthrown in February - are already working with aid agencies to help the victims of the storm.
When Jeanne hit, Haiti was already struggling to deal with the political instability, and the aftermath of serious floods in May.
Heavy deforestation has left Haiti particularly vulnerable to floods and landslides, correspondents say.
WFP trucks have been trying to reach the worst-affected areas, though they have been struggling to get through.
The British charity Oxfam said it was sending water engineers and food security experts on Wednesday to assess the extent of the damage.
A spokeswoman told BBC News Online that the risk of disease made the most pressing need sanitation and the distribution of clean water.
But she said it was likely that food shortages would become an issue too - "both the distribution of supplies in the short-term, and the rehabilitation of crops damaged in the flooding, in a country where the majority of people are dependant on agriculture for a living".
NORTHERN HAITI UNDER WATER
1. Waters have begun to recede in Gonaives, where about 175,000 people are affected - and 600 people are believed to have died.
2. Port-de-Paix city is still reported to be flooded in places, and nearby plantations under water. At least 40 bodies have been found in this area.
3. Aid agencies say the island of La Tortue was not hit as badly as at first thought.