The powerful Category 3 hurricane, the fiercest Caribbean storm in nearly a decade, whipped Cuba and Haiti with 140 mile-per-hour (230 kph) winds and torrential rains on Tuesday, pummelling towns and destroying livestock, crops and homes.
In the United States, more than 1.5 million people were urged to evacuate the south-eastern coast and Florida Governor Rick Scott warned residents to prepare for a possible direct hit that could be catastrophic.
Hundreds of thousands of people had been evacuated from the path of Matthew, which caused severe flooding and killed four people in the Dominican Republic as well as at least 22 in Haiti. The two countries share the island of Hispaniola.
The storm carved a path of devastation through south-western Haiti, dumping boats and debris on coastal roads hit by surging seas and flooding residential areas heavily.
Some 80 percent of homes were damaged in Haiti's Sud Department, which has a population of more than 700,000, a government official said in a meeting with UN officials. Some 11,000 people were in shelters in the province.
In the town of Jeremie, people were cooking and sleeping outside because most houses were either knocked down or severely damaged. Similar scenes were reported across the coastal towns of the south.
Haiti, the poorest country in the Americas, had been set to hold a repeatedly postponed presidential election on Sunday, but the country's electoral council delayed it again in the aftermath of Matthew. No new date has yet been set.


