The World Meteorological Organization (WMO) warned on Tuesday of catastrophic conditions in Jamaica as Hurricane Melissa makes landfall, bringing winds gusts exceeding 300 kilometres per hour, flash floods, and landslides, marking the worst storm to hit the island this century.

"It's a catastrophic situation expected in Jamaica," WMO tropical cyclone specialist Anne-Claire Fontan said at a Geneva press briefing. "For Jamaica, it will be the storm of the century for sure."

She said that storm surges of up to fourmeters were expected during the day and that rainfall was set to exceed 70 centimetres or about twice the amount expected normal the entire rainy season. "It means there will be catastrophic flash flooding and landslides," she said.

The International Federation of the Red Cross (IFRC) is bracing for up to 1.5 million people in Jamaica to be directly affected by the storm.

"Today will be very difficult for tens of thousands, if not millions of people in Jamaica," IFRC's Necephor Mghendi said via video link from Port of Spain.

"Roofs will be tested, floodwaters will rise, isolation will become a harsh reality for many."

Over 800 shelters have been set up for evacuees from the worst-hit areas, he added.

"The main priority was to get people out of harm's way to reduce the number of casualties."

(Reporting by Emma Farge, editing by Kirsti Knolle)