Hurricane Beryl has strengthened into a "potentially catastrophic" category 5 storm as it moved across the eastern Caribbean, putting Jamaica near its path after downing power lines and flooding streets elsewhere.

Beryl brings an unusually fierce and early start to this year's Atlantic hurricane season.

By 11.00 AST (0300 GMT) on Monday, Beryl, packing winds of up to 160mph (257km/h), was about 840 miles (1352km) east-southeast of Kingston, the Jamaican capital, the US National Hurricane Center (NHC) said.

The storm struck the Caribbean region earlier in the day as the earliest Category 4 storm on record, rated on the five-point Saffir-Simpson scale.

"Beryl is now a potentially catastrophic Category 5 hurricane," the NHC said.

It added that Beryl was expected to bring life-threatening winds and a storm surge to Jamaica later this week.

The storm could dump 4 inches to 8 inches (100mm to 200mm) of rain on Wednesday, rising to as much as 12 inches (310mm) in some areas, it said.

On its way, Beryl is expected to soak the island of Hispaniola on Tuesday in 2 inches to 6 inches (50mm to 150mm) of rain, as it moves west-northwest at nearly 22mph (35km/h), the Miami-based hurricane center said.

The aftermath of Hurricane Beryl in Barbados. – Reuters

Jamaica issued a hurricane warning, while tropical storm warnings were in effect for parts of the southern coasts of the Dominican Republic and Haiti.

At the Chillin' restaurant in Kingston, waiter Welton Anderson said he felt calm despite the hurricane's approach.

"Jamaicans wait until the last minute," he said. "The night before or in the morning, the panic sets in. It's because we're used to this."

Across other islands in the eastern Caribbean, residents had boarded up windows, stocked up on food and fuelled up cars as the storm approached.

Earlier, vehicles were seen driving through a flooded boardwalk in Bridgetown, Barbados.

The St Vincent community of Prospect reported roofs ripped off buildings and power cuts in some areas.

In Grenada, power was down islandwide.

Hurricane Beryl takes aim at southeastern Caribbean as a Category 4 storm. – AP

Officials in Mexico began to prepare for Beryl's arrival this week, with the federal government urging "extreme caution" on authorities and people.

Mexico is already assessing damage in its states of Oaxaca and Veracruz from heavy rain brought by former tropical storm Chris.

"What worries us is that basins are already saturated," said Cutberto Ruiz, chief of meteorology at Oaxaca's civil protection agency. "Then, with minimal rain … rivers will rise."

Scientists see the powerful hurricane Beryl as a harbinger of an unusually active hurricane season made possible by record high temperatures in the Atlantic Ocean.

Beryl jumped from a Category 1 to a Category 4 storm in less than 10 hours, said Andra Garner, a meteorologist based in New Jersey.

Hot water fuelling Hurricane Beryl's explosive growth. – AP

Scientists have already predicted that events like Beryl will grow more likely, added Garner, whose research has shown rising water temperatures have made it more than twice as likely for weak storms to grow into major hurricanes within less than 24 hours.

On the island of Tobago, a hotel and tourism group said limited damage had been reported to hotel properties.

"The eastern side of the island got the most battering and the seas remain dangerous," said Curtis Douglas, president of the All Tobago Fisherfolk Association.

"Fisherfolk got sufficient warning and were able to remove their boats from the water."

The projected path of Hurricane Beryl. – Reuters