Matthew briefly reached the top hurricane classification, Category 5, and was the strongest Atlantic hurricane since Felix in 2007.
The US National Hurricane Centre in Miami said its winds had slipped to a still-devastating 155mph and it was expected to reach the eastern part of Jamaica on Monday.
Jamaicans began clearing out store shelves as they stocked up emergency supplies and on Friday Prime Minister Andrew Holness called an urgent meeting of Parliament to discuss preparations for the storm.
“I left work to pick up a few items, candles, tin stuff, bread,” 41-year-old Angella Wage said at a crowded store in the Half Way Tree area of the capital, Kingston. “We can never be too careful.”
Evan Thompson, director of Jamaica’s National Meteorological Service, said:“We do consider it serious. We are all on high alert.”
Jamaicans are accustomed to intense tropical weather but Hurricane Matthew looked particularly threatening.
At its peak, it was more powerful than Hurricane Gilbert, which made landfall on the island in September 1988 and was the most destructive storm in the country’s modern history.
“Hurricane Matthew could rival or possibly exceed Gilbert if the core of the strongest winds does actually move over Jamaica,” said Dennis Feltgen, a meteorologist and spokesman for the hurricane centre in Miami.
“There is no certainty of that at this point.”
Matthew was expected to bring heavy rainfall especially to the eastern tip and higher elevations, which could trigger flooding and landslides, Thompson said.
Forecasters said rainfall totals could reach 10 to 15 inches, with isolated maximum amounts of 25 inches in Jamaica and southwestern Haiti.
Kingston is in the southeastern corner of Jamaica and is expected to experience flooding. The government issued a hurricane watch on Friday, and a tropical storm watch was issued for Haiti’s southwest coast for the southern border it shares with the Dominican Republic to the capital of Port-au-Prince.
It brought extremely high tides, storm surge and heavy rain to Colombia, prompting authorities to declare an alert as local TV broadcast images of cars and tree trunks surging though flooded streets.
Matthew caused at least one death, with officials in St Vincent reporting that a 16-year-old boy was crushed by a boulder as he tried to clear a blocked drain.