Hurricane Matthew grew into a powerful Category 4 storm on Friday as it crossed the Caribbean Sea on a course that could have it pounding Jamaica within days.

The center of the hurricane was projected to pass just to the east of Jamaica early Monday, but the storm was large enough that it could affect the entire island, and the first effects of the storm may be felt starting Saturday, said Evan Thompson, director of the National Meteorological Service.

"We do consider it serious," Thompson said. "We are all on high alert."

Jamaica activated its National Emergency Operations Center and Prime Minister Andrew Holness called an urgent meeting of Parliament to discuss preparations for the storm. People cleared out store shelves as they stocked up emergency supplies.

"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. "We can never be too careful."

Jamaicans are accustomed to intense tropical weather but Hurricane Matthew looked particularly threatening. With wind speeds of 150 mph (242 kph), 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 the Jamaica," said Dennis Feltgen, a meteorologist and spokesman for the U.S. National Hurricane Center in Miami. "There is no certainty of that at this point."

Hurricane Matthew was expected to bring heavy rainfall especially to the eastern tip and higher elevations, which could trigger flooding and landslides, Thompson said.

Forecasters at the National Hurricane Center said rainfall totals could reach 10 to 15 inches (25 to 38 centimeters) with isolated maximum amounts of 25 inches (63 centimeters) in Jamaica and southwestern Haiti.

The Jamaican capital, Kingston, is in the southeastern corner of Jamaica and was expected to experience flooding. The government issued a hurricane watch on Friday afternoon, and a tropical storm watch was issued for Haiti's southwest coast form the southern border it shares with the Dominican Republic to the capital of Port-au-Prince.

As of 8 p.m. EDT, the storm was centered about 80 miles north-northwest of Punta Gallinas, Colombia, and about 440 miles southeast of Kingston, Jamaica. It was moving west-southwest at 9 mph.

Hurricane-force winds extended outward up to 35 miles from the center and tropical-storm-force winds extend outward up to 195 miles.

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 in coastal areas. Local media in La Guajira province reported that one person died in flooding.

Matthew caused at least one death when it entered the Caribbean on Wednesday, with officials in St. Vincent reporting a 16-year-old boy was crushed by a boulder as he tried to clear a blocked drain.