Haiti's interim President Jocelerme Privert has called for rapid, effective and coordinated action to help people affected by Hurricane Matthew.
Privert held a meeting on Friday to assess the damage of the hurricane, the Haiti Libre daily reported.
Southern Haiti bore the brunt of the damage, suffering from severe flooding, high waves along the coast, as well as lashing wind.
According to the daily, the United Nations Environment Programme said the waves and strong wind that accompanied Hurricane Matthew destroyed or damaged nearly 90 percent of the houses along the coastal area of the South department.
The central government put the death toll at more than 300 as receding waters revealed the extent of the damage and allowed rescue workers to access areas that were previously cut off. But several international news agencies placed the number at about 850, citing regional officials in Haiti's South department.
The hurricane left Haiti's already fragile infrastructure in tatters, washing away a key bridge that connected the capital city of Port-au-Prince with the Southern department.
Access by land to the South department has been restored through a detour over La Digue river, the daily said.
The United Nations estimated some 350,000 Haitians are in need of immediate assistance to stave off the spread of disease, such as cholera, which has already claimed some 9,000 lives since an outbreak following a devastating earthquake in 2010.
The World Food Programme (WFP) was deploying logistics and assessment teams in coordination with the Haitian government and international agencies to bring in much needed relief.
WFP teams were also in Haiti to determine the hurricane's wider impact on food and nutrition security.
"At the time the hurricane struck Haiti, the agency had already prepositioned sufficient emergency supplies to feed up to 300,000 people for a month," deputy UN spokesman Farhan Haq told a daily news briefing.
The UN Children's Fund (UNICEF) said that some 500,000 children lived in southern Haiti, the worst-hit parts of the country, said Haq. "A UNICEF team has reached Les Cayes and has reported massive flooding."
It had prepositioned emergency supplies with national authorities to reach up to 10,000 people, he said.
"Additional water and sanitation supplies, such as water purification tablets, water bladders and plastic sheeting, have been dispatched to the most affected departments in the westernmost tip of Haiti."
UNICEF said it needs at least 5 million U.S. dollars to meet children's most pressing needs, including restoring health services to help prevent and treat malnutrition among young children and provide essential vitamins and anti-diarrhoea treatment; setting up temporary learning spaces; and supporting child protection services to protect children from violence, exploitation and abuse, he added.
France, in cooperation with European partners and allies, is mobilizing efforts to provide Haiti with emergency aid.
French President Francois Hollande said Friday that the most urgent need now is to provide drinking water to the population and prevent health risks.
Paris will provide water purification equipment, medical kits, and first-aid equipment, the president's office said in a statement.
The International Federation of Red Cross and Red Crescent Societies (IFRC) on Friday launched an emergency appeal for 6.8 million dollars to provide medicines, shelters, water and sanitation facilities to 50,000 people in the storm-ravaged southwest of Haiti.
"This vulnerable nation has been hit again by a huge disaster that requires substantial international support," said Ines Brill, IFRC head of delegation in the Latin Caribbean.
Matthew, which also hit Cuba, the Dominican Republic and the Bahamas, went on to lash the east coast of the U.S. state of Florida through Friday.
