Hurricane Matthew has left 108 people dead in Haiti, the interior minister has told AFP news agency.
One local official, speaking to AFP, said 50 people had died in the southern town of Roche-a-Bateau alone.
New images from remote and cut off areas in the south-west of the country show scenes of devastation.
The hurricane has again been upgraded to a Category Four storm, the second highest hurricane classification, as it heads for the US state of Florida.
Hurricane Matthew – the most powerful Caribbean storm in nearly a decade – is currently pounding the Bahamas, after slicing through Haiti and Cuba.
At least 140 people have died across the region since it first hit landfall in Haiti on Tuesday, Reuters reported, with Haiti suffering the worst losses.
Most of the fatalities were in towns and fishing villages around the Tiburon peninsula, with many killed by falling trees, flying debris and swollen rivers.
The storm passed directly through the peninsula, driving the sea inland and flattening homes with winds of up to 145 mph (230 kph) and torrential rain on Monday and Tuesday.
“I’ve never seen anything like this,” said Louis Paul Raphael, a central government representative in Roche-a-Bateau.
What were the most recent deadly Atlantic storms?
Hurricane Matthew is already the deadliest Atlantic storm since 2012, when Hurricane Sandy directly killed at least 147 people.
Sandy was a category three storm. Matthew is a category four, after being downgraded from category five – the highest classification.
Category five hurricanes are rare, and not always the most deadly. Circumstances, rather than wind speed, dramatically affect how dangerous a storm is.
In 2005, Hurricane Katrina was a category three when it made landfall in the United States. It left 1,800 people dead, and was the costliest storm in US history with damage estimated at $108 billion (£85bn).
The last category four storm in the Atlantic, Hurricane Joaquin in October 2015, killed 34 people – 33 of which were on board the cargo ship El Faro, which sank during the storm.
At least 130 people were killed in Honduras and Nicaragua during the last category five Atlantic storm – Hurricane Felix – which hit Central America in 2007.
The true scale of the devastation in Haiti was only being uncovered on Thursday, after a key bridge collapsed on Tuesday, meaning the south-west was largely cut off.
An earlier death toll given by Haiti’s civil protection service stood at 23, but as emergency services gained access to some of the more remote areas on Thursday, the number rose rapidly to more than 100.
“The whole southern coast of Haiti, from the town of Les Cayes to Tiburon, is devastated,” Pierre-Louis Ostin told the AFP news agency.
More than 29,000 homes were destroyed in the hard-hit Sud department alone, and more than 20,000 people have been displaced, local authorities said.
Across the country, there are some 350,000 in need of assistance, according to the UN Office for the Coordination of Humanitarian Affairs.
It was “pretty much wiped out from the seaboard all the way to the cathedral”, a radio host in Haiti’s capital of Port-au-Prince told the BBC on Thursday.
“The devastation that we are seeing is horrible…The town is really in dire straits and it’s very, very bad down there.”
Early assessments carried out by authorities showed nearly 2,000 homes were flooded and at least 10 schools were damaged across the country, the French Itele website reports.
Haiti’s presidential election due this weekend has been postponed because of the hurricane.
The country is one of the world’s poorest, with many residents living in flimsy housing in flood-prone areas.
Four people also died in the storm in the neighbouring Dominican Republic on Tuesday.
Why Haiti is vulnerable to disasters
Hurricane Matthew has left a trail of destruction across the Caribbean, but nowhere has the devastation been more severe than in Haiti.
The poorest country in the Americas, Haiti has long been particularly vulnerable to natural disasters. Six years after an earthquake killed more than 200,000 people and displaced 1.5 million, tens of thousands of quake victims still live in temporary shelters.
More than half of Haiti’s city-dwellers live in overcrowded shanty towns that take the full force of any earthquake, hurricane, or disease outbreak. An ongoing cholera epidemic, triggered by the arrival of UN troops after the 2010 quake, has killed thousands of people.
Massive deforestation has also led to soil erosion, leaving hillside huts and poorly-built houses in the capital, Port-au-Prince, dangerously exposed. The consequence in rural areas, where many depend on small plots of land for their food, is that topsoil is often washed away.
Political instability and corruption have been a factor. Without effective government for decades, Haiti currently ranks 163rd out of the 188 countries on the UN Human Development Index. It spends little on storm defences.