Americans meanwhile girded for a taste of nature's fury, with Matthew forecast to strengthen again over the next couple days.
Florida and South Carolina as well as parts of North Carolina and Georgia have declared states of emergency. South Carolina said it would start evacuating 1.1 million people from its coast Wednesday and try to get them at least 100 miles inland.
"It's not going to be a fast evacuation. It could take up to several hours," South Carolina Governor Nikki Haley said. "If you can leave early, do that."
The storm is expected to move across the Bahamas through Thursday and near the coast of Florida Thursday evening, the NHC said.
Matthew was forecast to dump 15 to 25 inches of rain over southern Haiti with up to three feet possible in isolated areas, and has been blamed for triggering mudslides.
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The key port of Les Cayes, the country's third city is "very seriously damaged," said Hervil Cherubin, Haiti director for the aid group Heifer International. "Most roofs of houses, shops, gas stations are all gone."
The country is home to almost 11 million people, with thousands still living in tents after the massive earthquake in 2010.
Matthew already holds the longevity record for a Category Four and Five hurricane in the Caribbean, according to meteorologist Philip Klotzbach from Colorado State University.
The United States Agency for International Development (USAID) dispatched an elite disaster response team to the Bahamas, Haiti and Jamaica.
It is also sending some $400,000 in assistance to aid groups in Haiti and Jamaica and emergency relief supplies.
The Pentagon said 700 family members of personnel have been evacuated from the US naval base in Guantanamo Bay, on Cuba's eastern tip, to Florida.
President Barack Obama postponed a trip to South Florida, where he had planned to attend a campaign event in support of Democratic presidential candidate Hillary Clinton.
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