Hurricane Matthew is speeding towards Jamaica and Cuba with winds of up to 160 miles per hour, making it the Caribbean's strongest storm in nine years, according to forecasters.
The US National Hurricane Center (NHC) designated it as a Category 5 storm - the strongest on the Saffir-Simpson scale, before grading it down to Category 4.
It will reach Jamaica's southern coast on Monday, where it could do large amounts of damage including wrecking houses, forecasters said.
Meteorologist Eric Holthaus said it could be the strongest hurricane since records began in 1851.
"The government is on high alert," said Robert Morgan, director of communications at the prime minister's office.
"We hope that the hurricane does not hit us, but if it does hit us, we are trying our very best to ensure that we are in the best possible place."
Over the past few days, Jamaicans have been rushing to local shops to stock up on provisions.
Sandy in 2012 was the last major hurricane in the region. Hurricane Felix in 2007 resulted in more than 100 deaths across the Caribbean and Central America, as well as significant damage to crops.