Haiti faces a crisis that requires a "massive response" from the international community, the United Nations has said, with at least 1.4 million people needing emergency aid after Hurricane Matthew.
The storm killed almost 1,000 people in the impoverished Caribbean nation, with that toll expected to rise as rescue workers reach previously inaccessible areas.
Matthew, the most powerful Atlantic storm since 2007, last week levelled homes, fouled water sources and killed livestock, leaving victims pleading for help to arrive quickly.
"Some towns and villages have been almost wiped off the map," UN Secretary-General Ban Ki-moon told reporters.
The United Nations has launched a $120m flash appeal to cover Haiti's needs for the next three months.
Haiti's interim president has warned his country risks "real famine" following the "apocalyptic destruction" of Hurricane Matthew.
Jocelerme Privert said famine could take hold within three to four months if the situation was not managed properly.
It comes as UN Secretary General Ban Ki-moon called for a "massive response" to help the country.
After pummelling Haiti on October 4 as a monster Category 4 storm, packing winds of 230km/hr, Matthew slammed into the southeastern United States, where it killed at least 20 people.
Hundreds of people were rescued by boat and helicopter as floodwaters inundated towns in the state of North Carolina on Monday, and officials warned that life-threatening flooding from swollen rivers would continue for days.
The category-four storm is believed to have killed as many as 900 Haitians.
It has also wiped towns and villages off the map, destroying tens of thousands of homes, crops and food reserves.
Mr Privert said the loss was "amazing", saying food, water and medicine was immediately needed.
In Haiti, more than 300 schools have been damaged, while crops and food reserves were destroyed, Ban said.
UN aid chief Stephen O'Brien said that the hurricane had triggered the worst humanitarian crisis in the country since the 2010 earthquake.
Nearly 300,000 Haitians are in shelters across the country, and damage to roads and communications has hampered deliveries of supplies.
"I understand of course the frustration," Jean-Luc Poncelet, the country representative for the UN's World Health Organization, said after arriving at the airport outside Jeremie, one of the worst-hit cities.
"When you have no means of communication, no radio, no telephone, no roads and even a helicopter can't land - this is what explains the massive delay," he said.
The UN's World Food Programme tapped into food stocks previously set aside for schools to feed hundreds of desperate families, spokesman Alexis Masciarelli said.
"But the concern is if we don't take action now for the longer impact... three to four months when the foods stop coming we are going to have a real famine."
He described seeing "apocalyptic" destruction. "What I saw with my eyes yesterday will take a lot of effort to work on the reconstruction part of what has been destroyed," he said.
Matthew was the strongest hurricane to hit the region in a decade.
The UN has launched an emergency appeal for nearly $120m (£97m) in aid to cover the next three months.
Speaking to reporters on Monday, Mr Ban said: ""Hundreds have died; at least 1.4 million people need assistance at this time.
"Some towns and villages have been almost wiped off the map; crops and food reserves have been destroyed; at least 300 schools have been damaged,"
The UN humanitarian agency issued the appeal to help provide "life-saving assistance and protection" for 750,000 people in south-western Haiti over the next three months.
Officials were still struggling to reach the hardest-hit areas, the agency said, with communities in need of food, clean water and clothing.
There were growing fears that flooding could cause a cholera outbreak similar to that after the 2010 earthquake.
The waterborne disease reached the island via Nepalese UN troops, causing the deaths of nearly 10,000 people.
A treatment centre in the town of Jeremie has become overcrowded with not enough beds for patients, and some of them were being forced outside, reports said. Many of the cases involved children.
Other countries including France and the US have pledged to send aid. The Red Cross has launched an emergency appeal for $6.9m (£5.6m) and Unicef said it needed at least $5m to meet the immediate needs of 500,000 affected children.
Meanwhile, at least 21 have been killed by Matthew in the US, 10 of them in North Carolina, most of them swept away by flood waters.
"Hurricane Matthew is off the map. But it is still with us. And it is still deadly," Governor Pat McCrory said.
There were also four deaths in Florida and three each in Georgia and South Carolina. One death was reported in Virginia. Nearly 1.2 million people were without power.
US army helicopters were unloading boxes of supplies from the US Agency for International Development to be stored by the UN in Jeremie before being taken to other parts of the south.
Honduras, which maintains a force of 60 troops in Haiti as part of a UN peacekeeping mission, was sending a planeload of aid on Tuesday, along with 50 military officers to help the victims, President Juan Orlando Hernandez said.
But getting aid to Haitians now reduced to drinking unclean water and living in roofless houses will be challenging.
On a road crossing the mountainous centre of the peninsula, some villagers blocked roads in an effort to stop aid convoys from passing through without delivering supplies.
Haiti is also grappling with a worsening cholera outbreak in the storm-hit areas.
Matthew came as Haitians were already struggling with the intestinal disease spread by contaminated food and water, with more than 500 new cases each week.
UN peacekeepers have been blamed for introducing the disease to Haiti, where it has killed 10,000 people since October 2010.While some towns and villages reported an apparent spike in infections since the storm, Poncelet said "the number of cases of cholera that we have confirmed are low".
He declined to give a number, but said there were "tens" of cases in one area of the peninsula.
While evaluation teams were working to get a precise picture of the health situation, medical supplies were being brought in, he said.
Mourad Wahba, the UN humanitarian coordinator in the country, urged aid organisations to focus on delivering supplies to smaller rural communities, where many families survive on subsistence farming and have had all their crops washed away.
If aid is only delivered to cities such as Jeremie and Les Cayes, villagers will flock there for supplies and never leave, leading to overcrowding.
"We must think about developing a plan, to coordinate support and deliver it where it's most needed and not where it's easiest to access," Wahba said.
When Hurricane Matthew dumped torrential rains on North Carolina, thousands of people found themselves suddenly trapped in homes and cars. Rescuers in Coast Guard helicopters plucked some of them from rooftops and used military vehicles to reach others, including a woman who held on to a tree for three hours after her car was overrun by flood waters.
In another dramatic rescue, a woman with her small child perched on the roof of her car had to be helped to safety as the waters rose around them, underscoring how quickly Matthew wreaked havoc 160 kilometres or more inland after sparing much of the Southeastern coast the catastrophic damage once feared.
The storm killed more than 500 people in Haiti and at least 17 in the U.S. — nearly half of them in North Carolina. Gov. Pat McCrory said authorities were searching for five people and feared they may find more victims. The problems were far from over as all that rain — more than a foot in places — flows into rivers and downstream, likely causing days of major flooding in many of the same places devastated by a similar deluge from Hurricane Floyd in 1999.
“Hurricane Matthew is off the map. But it is still with us. And it is still deadly,” McCrory said.
More than a million people in South Carolina and North Carolina were without power, and at least four separate sections of Interstate 95 — the main artery linking the East Coast from Florida to Maine — were closed in North Carolina.
The ferocity of the rain caught people by surprise.
“The forecast said it wasn’t supposed to be anything major. Just rain and wind. Well, considering what happened weeks prior with the rain and combined with this, Mother Nature’s at its best,” said Lamont England, who was trying Sunday to get to his parents’ home in Fayetteville.
In Wilson County, rescuers were called when a 63-year-old woman didn’t make it home from work. They heard her cries for help while riding on top of a Humvee, and when they couldn’t get her with a rope, a National Guard soldier swam to her, staying until a rescue boat arrived, Emergency Management Director Gordon Deno said.
Even animals had to be saved. WRAL-TV showed a dog swimming around floodwaters Saturday. McCrory said he and his wife were riveted by the coverage and relieved to find out from the Coast Guard that the dog managed to get into a tree and rescue it.
Most of the dead were swept away by flood waters. The governor said there were rural areas that search and rescue teams hadn’t been able to make it to and places that flooded overnight.
“There could be some backroads where we had people swept away. I’m praying that is not going to be,” McCrory said.
The rainfall totals were staggering: Nearly 38 centimetres in Fayetteville and 20 centimetres in Raleigh. McCrory warned that cities along rivers in eastern North Carolina needed to be prepared for days of flooding. The Lumber River in Lumberton was 4 feet above its record level Sunday afternoon and was forecast to remain there for at least five days.
Shortly before daybreak, the hurricane was downgraded to a post-tropical cyclone. As of 2 p.m. EDT, the storm was centred about 241 kilometres east of Cape Hatteras, North Carolina, moving out to sea. It still had hurricane-force winds of 120 km/h.
Elsewhere along the Atlantic coast, things were slowly returning to normal. Much of Savannah, which had 43 centimetres of rain, was still without electricity. About 150 people stood in line for a grocery store to open like it was a Black Friday sale.
Debbie Berta said she waited more than an hour to get propane gas for her grill. She also wanted “bread, potatoes, eggs — and a piece of sanity.”
The fearsome storm then sideswiped hundreds of miles of the U.S. coastline from Florida through Georgia and the Carolinas, its eye staying far enough offshore that the damage in many places along the coast was relatively modest, consisting mostly of flooded streets, flattened trees and blown-down signs and awnings. A shift of just 20 or 30 miles could have meant widespread devastation nearer the ocean.
An estimated 2 million people in the Southeast were ordered to evacuate their homes as Matthew closed in.
In addition to the eight deaths in North Carolina, there were four in Florida, three in Georgia and two in South Carolina. Some were killed by falling trees, others by carbon monoxide fumes from a generator. One 66-year-old man near Columbia, South Carolina, died at a nursing facility when he got pinned under his electric wheelchair in water after the heavy rains.
Property data firm CoreLogic projected that insured losses on home and commercial properties would amount to $4 billion to $6 billion (U.S.), well below Hurricane Katrina’s $40 billion and Superstorm Sandy’s $20 billion.