Tropical storm Jeanne swept north of Haiti during the weekend, drenching the impoverished Caribbean nation of eight million, inundating cities and sending deadly mudslides through towns and villages.
Officials at the Office of Civil Protection in Port-au-Prince said 709 deaths had been confirmed in the flood-stricken areas and 1050 people were missing.
Most of the dead were in the swamped coastal city of Gonaives and the toll was likely to rise as relief workers reached areas isolated by the floods.
"As the water recedes we begin to see bodies emerge from the mud," said Fernando Arroyo, a UN official in Gonaives.
"There are bodies scattered on the roads, in the streets."
The dead were to be buried in mass graves as soon as heavy machinery arrived, to avert an outbreak of disease, he added.
Relief supplies have started to reach the worst-hit areas, but the pace has been slowed by waterlogged roads and worries about security in a country that is still unstable after an armed revolt ousted president Jean-Bertrand Aristide in February.
"I lost five people in the floods and I don't have anything, no water, no food, nothing," said one stunned Gonaives resident, Mercidieu Pierre-Andre, 49.
Interim PM Gerard Latortue has
pledged to provide all possible aid
Water was still waist high in places and mud on the windows of homes illustrated a desperate tale of rising water that sent people climbing on to their roofs to survive.
Some were still camped on the roofs of mud-filled homes on Tuesday, sleeping under plastic tarps on the only dry spots they could find.
Thousands of people were in shelters, some 600 of them finding refuge in the cathedral in Gonaives. Others who lost their homes and families tried to flag down trucks in the hope of catching rides to other cities to begin life anew.
UN officials said drinking water was urgently needed.
The World Food Programme sent 12 trucks with 40 tonnes of food to Gonaives and hoped to start handing it out by Wednesday after ensuring that distribution points would be secure, said regional WFP spokesman Alejandro Chicheri.
Haiti, the poorest country in the Americas, is chronically vulnerable to flooding because of widespread deforestation. Flooding in May killed about 2000 people.
"I lost five people in the floods and I don't have anything, no water, no food, nothing"
Interim Prime Minister Gerard Latortue visited flooded areas of Gonaives and the northern city of Port-de-Paix, and pledged to provide all possible aid.
"We don't have much means but we'll bring what we have," he told a group of Port-de-Paix residents.
At the United Nations, interim President Boniface Alexandre appealed for world aid at the opening of the annual General Assembly session.