Hurricane Beryl was hurtling towards Jamaica on Tuesday as a monster Category 5 storm, after killing at least five people and causing widespread destruction in a deadly sweep across the southeastern Caribbean.

Though expected to weaken slightly later on Tuesday, the hurricane is still on track to slam into Jamaica on Wednesday as a "near-major" storm, bringing life-threatening winds, storm surge, rain and flash flooding, the US National Hurricane Centre (NHC) warned.

Beryl has already razed parts of the southeastern Caribbean as a Category 4 storm, killing at least three people in Grenada, one in St Vincent and the Grenadines, and one in Venezuela, officials said.

The Prime Minister of Grenada, Dickon Mitchell, said the island of Carriacou – which the NHC said took a direct hit from the storm – has been all but cut off, with houses, telecommunications and fuel facilities there flattened by 90 kilometres per hour winds.

"We've had virtually no communication with Carriacou in the last 12 hours except briefly this morning by satellite phone," he told a news conference.

The 35-square kilometre island is home to around 9,000 people. At least two people there died, Mitchell said, with a third killed on the main island of Grenada when a tree fell on a house.

The family of UN climate chief Simon Stiell is among the residents of Carriacou. His office said his parents' property was damaged.

Some 90 percent of the homes along with the airport on Union Island, in St Vincent, have also been damaged or destroyed, Prime Minister Ralph Gonsalves said. The three-square mile island has a population of around 3,000.

Gonsalves said the storm also killed one person on another island, Bequia.

Beryl "has left in its wake immense destruction, pain and suffering," he said in a Facebook video late on Monday.

One man also died when swept away by a flooded river in the state of Sucre on Venezuela's northeastern coast, officials there said.

Barbados appeared to have been spared the worst but was still hit with high winds and pelting rain, although officials reported no injuries so far.

Martinique was also largely spared, with damage to boats and some flooding in downtown Fort-de-France.

Experts say it is extremely rare for such a powerful storm to form this early in the Atlantic hurricane season, which runs from early June to late November.

Beryl is the first hurricane since NHC records began to reach the Category 4 level in June, and the earliest to reach Category 5 in July. (AFP)