Hurricane Melissa, already a major category 4 storm, gathered steam Sunday as it took aim at Jamaica and other parts of the Caribbean, with forecasters predicting catastrophic flooding and urging residents to seek shelter immediately.

Melissa has already been blamed for at least four deaths in Haiti and the Dominican Republic this week, as its outer bands brought heavy rains and landslides.

The storm is moving at a worryingly slow pace -- just five miles (seven kilometers) an hour -- meaning areas in its path could see punishing conditions for far longer than a hurricane that passes by more quickly.

The US National Hurricane Center (NHC) said Melissa was packing maximum winds of about 145 miles (230 kilometers) per hour -- and would likely intensify into a top-level category 5 storm later Sunday.

Up to 40 inches (about a meter) of rainfall could hit parts of Jamaica, Haiti and the Dominican Republic, sparking flash flooding and more landslides.

"This extreme rainfall potential, owing to the slow motion, is going to create a catastrophic event here for Jamaica," NHC Deputy Director Jamie Rhome said in a webcast briefing.

"You need to just be wherever you're going to be and be ready to ride this out for several days," Rhome said.

"Conditions will deteriorate really, really rapidly here in the next few hours. Don't be out and about after sunset."

A 79-year-old man was found dead in the Dominican Republic after being swept away in a stream, local officials said Saturday. A 13-year-old boy was missing.

In neighboring Haiti, the civil protection agency reported the deaths of three people caused by storm conditions.

"You feel powerless, unable to do anything, just run away and leave everything behind," Angelita Francisco, a 66-year-old homemaker who fled her neighborhood in the Dominican Republic, told AFP through tears.

Floodwater had inundated her house, causing her refrigerator to float away as trash bobbed around the home.

'Cannot bet against Melissa'

Jamaica was expected to see deteriorating conditions from Melissa through Sunday, with landfall not expected until late Monday or early Tuesday.

"Seek shelter now," the NHC advised residents.

Winston Moxam was hurrying to prepare his home for the coming storm, telling AFP if "I lose my roof, I lose a whole lot of things."

He said he was particularly worried by warnings it could be worse than 1988's Hurricane Gilbert, which left over 40 dead in Jamaica and killed hundreds more around the Caribbean and in Mexico.

The international airport in Kingston closed late Saturday, as did all seaports.

Government official Desmond McKenzie told a briefing that storm shelters had been activated across the island nation.

"There is nothing more we can do as a government but to beg and beseech persons to heed the warning  -- and if it will help, I will go on my knees," he said.

"This is one bet you cannot win. You cannot bet against Melissa," he warned.

At 2100 GMT, the hurricane was located about 115 miles south-southwest of Kingston and 295 miles south-southwest of Guantanamo Bay, Cuba.

After passing over Jamaica, the storm was forecast to head north and cross over eastern Cuba on Tuesday night, while continuing to bring rains and heavy winds to Haiti and the Dominican Republic.

The Dominican Republic's emergency operations center has placed nine of 31 provinces on red alert due to risk of flash floods, rising rivers and landslides.

Melissa is the 13th named storm of the Atlantic hurricane season, which runs from early June to late November.

The last major hurricane to impact Jamaica was Beryl in early July 2024 -- an abnormally strong storm for the time of year.

Beryl brought downpours and strong winds to Jamaica as it moved past the island's southern coast, leaving at least four people dead.