The most powerful Caribbean hurricane in nearly a decade has hit Haiti, bringing 230 kilometre per hour winds, heavy rain and dangerous storm surges.
Hurricane Matthew, a Category Four storm, made landfall at about 6am Haiti time, and is heading towards eastern Cuba.
The US National Hurricane Center (NHC) said Haiti was "getting everything a major hurricane can throw at them".
Reports from the southern coast spoke of communities under water and buildings stripped of roofs.
Marie Alta Jean-Baptiste, director of the country's Civil Protection Agency, told Associated Press: "It's much too early to know how bad things are but we do know there are a lot of houses that have been destroyed or damaged in the south."
One resident too ill to leave their home was killed when waves struck in the town of Port Salut.
Haiti's Interim President Jocelerme Privert said earlier that some people at sea or who had not "respected alerts" had died, but he gave no more details.
Haiti is one of the world's poorest countries and many of its 11 million residents live in areas prone to flooding and in flimsy housing. Matthew is expected to bring up to 102cm of rain to some parts as it moves north at about 15 kilometres per hour.
Social media footage from the southern coastal town of Les Cayes showed palm trees being bent sideways and buildings with roofs sheared off.
Speaking from Port-au-Prince, American journalist Jacqueline Charles said reports from Les Cayes spoke of people walking in water shoulder high, with relief workers saying that other coastal communities were also under water.
Fonie Pierre, director of Catholic Relief Services for Les Cayes, told AP: "Many people are now asking for help, but it's too late because there is no way to go evacuate them."
The mayor of Les Cayes, Jean Gabriel Fortune, posted tweets that included video showing damage in the Vernet area.
The mayor of Tiburon, Remiza Denize, spoke of large waves hitting the town: "Everyone is trying to find a safe place to protect themselves."
Ms Jean-Baptiste said that there had been a major landslide between Les Cayes and Tiburon.
A farmer in the town of Leogane, Milriste Nelson, said: "All the banana trees, all the mangoes, everything is gone."
Guantanamo Bay evacuation
Haitian officials said that about 1300 emergency shelters had been built, enough to accommodate 340,000 people. Both airports in Haiti are closed.
One local in Port-au-Prince said the community would unite in the face of the storm's danger.
"We are communicating amongst ourselves thanks to our own means. We will tell the people how the situation is. If things are bad then we will come together."
Unicef said more than four million children might be exposed to hurricane damage.
The UN children's fund representative in Haiti, Marc Vincent, said: "Waterborne diseases are the first threat to children in similar situations - our first priority is to make sure children have enough safe water."
An NHC statement said: "On the forecast track, the eye of Matthew will move near eastern Cuba later [on Tuesday], and move near or over portions of the south-eastern and central Bahamas [on Tuesday night] and Wednesday, and approach the north-western Bahamas on Wednesday night."
About 13,000 people were evacuated from high-risk areas in neighbouring Dominican Republic, which is also expected to get battered by rains and winds, according to the country's civil defence chief.
A hurricane alert is in place for six eastern Cuban provinces and residents are being moved from low-lying areas.
Some 700 spouses and children of US service members have been flown out of the Guantanamo Bay base, which is just 80km from where the storm could make landfall.
It is also predicted to hit the US east coast later in the week. Florida and parts of North Carolina have declared states of emergency.
Hurricane Matthew is the region's most powerful since Felix in 2007.