Hurricane Beryl intensified again into a "potentially catastrophic" Category 5 storm on July 2 as it moved across the eastern Caribbean, headed for Jamaica after downing power lines and flooding streets in the western Caribbean islands.

Beryl is the earliest ever recorded hurricane in the Caribbean seas after it strengthened from a tropical storm to a Category 4 hurricane in a mere 42 hours. Another hurricane of this strength, this early in the season, has only been seen once before in 1933, which is the only other time a hurricane has appeared east of the Caribbean. The average date for the first hurricane of the season is August 11. Scientists have attributed its rapid formation to record warm sea temperatures that are a result of the accelerating climate crisis.

By 11am local time on July 1 Beryl, packing winds of up to 257km/h (71.4m/s), was about 1,352 km east-southeast of Kingston, the Jamaican capital, the US National Hurricane Center (NHC) reported.

"Beryl is now a potentially catastrophic Category 5 hurricane," the NHC stated as quoted by Reuters, adding that it is expected to bring life-threatening winds and a storm surge to Jamaica later this week. The storm could dump 10 to 20 cm of rain on July 3, with some areas seeing a deluge of as much as 31 cm.

As Beryl moves west-northwest at nearly 35km/h, it is expected to soak the island of Hispaniola on July 2 with 5 to 15 cm of rain.

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

Locals in Jamaica were taking the storm warnings in their stride as they are used to hurricanes, although Beryl is more powerful than most. Category five is the most powerful on the Saffir-Simpson scale, although this year scientists warn that a never seen before Category 6 storm is possible.

Across other islands in the eastern Caribbean, residents have been boarding up windows, stocked up on food, and fuelled their cars in preparation for the storm.

In St. Vincent, the community of Prospect reported Beryl has ripped roofs off buildings and cut power in some areas, while in Grenada, power was down island-wide, according to a Reuters reporter.

In Mexico, officials began preparations for Beryl's arrival this week, urging "extreme caution" among authorities and residents. Mexico is also 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 early arrival of hurricane Beryl as a harbinger of a “hyperactive” hurricane season. There are usually half a dozen hurricanes each season, but this year scientists are predicting 17-25 named storms, of which eight to 13 could become hurricanes.