HOMESTEAD, Fla. — Hurricane Irma was downgraded to Category 4 status early Saturday as the storm slammed Cuba with maximum sustained winds of 155 mph, the National Hurricane Center confirmed.

As of 5 a.m. ET Saturday, the eye of the storm was still moving over Cuba's Camaguey Archipelago, the National Hurricane Center said. The center of the storm was located about 245 miles south-southeast of Miami and was moving to the west at 12 mph, the National Hurricane Center added.

Authorities pleaded with residents of the Florida Keys to evacuate in the few remaining hours before Hurricane Irma’s arrival, warning that storm surges and high winds pose a particular risk to the string of low-lying sandbar islands tailing off Florida’s southern tip. Officials also scrambled to provide fuel for hundreds of thousands of residents trying to flee northward or to local shelters.

"This is a catastrophic storm the state has never seen before," Florida Gov. Rick Scott said as he made another plea for residents to heed evacuation warnings. “If you are planning to leave and do not leave tonight, you will have to ride out this extremely dangerous storm at your own risk," he said, according to The Associated Press.

Miami International Airport announced on Twitter that "there were no scheduled flights for Saturday and Sunday," adding that the last flight departed late Friday night.

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Current tracking shows the center of the storm moving near Cuba's north coast on Saturday, near the Florida Keys early Sunday morning, and then traveling near the southwest coast of Florida on Sunday afternoon, the National Hurricane Center said.

Forecasters warned that its hurricane-force winds were so wide they could reach from coast to coast, testing the nation’s third-largest state, which has undergone rapid development and more stringent hurricane-proof building codes in the last decade or so.

The storm has killed at least 20 people since roaring out of the open Atlantic and chewing through a string of Caribbean islands. Four deaths were reported in the British Virgin Islands, nine on the French Caribbean islands of St. Martin and St. Barts, four in the U.S. Virgin Islands, and one each on the islands of Anguilla, Barbuda and the Dutch side of St. Martin.

In the Gulf of Mexico, Hurricane Katia made landfall late Friday north of Tecolutla, Mexico and weakened to a tropical storm, with winds reaching 45 mph, AP reported.

Early Saturday, Hurricane Jose maintained its Category 4 status over the Atlantic, about 240 miles east-southeast of the Northern Leeward Islands, moving roughly westward at 14 mph with maximum sustained winds reaching 150 mph.

Rice and Stanglin reported from McLean, Va. Contributing: Associated Press