President Joe Biden issued a stark warning Tuesday as Hurricane Milton speeds toward the state of Florida, saying it could be the worst to hit the southern US state in over 100 years. 

Biden urged residents to "evacuate now, now, now," saying forecasts indicate Milton "could be the worst storm to hit Florida in over a century."

"You should have already evacuated. It's a matter of life and death," he told residents in Milton's predicted path.

Milton was downgraded to a still dauntingly powerful Category 4 hurricane Tuesday, after hitting Category 5 wind speeds Monday. It is packing maximum sustained winds of 145 miles per hour (230 kilometers per hour) as it moves over the warm waters of the Gulf of Mexico.

Biden authorized an emergency declaration for Florida early Monday as the state continues to recover from Hurricane Helene, and braces for Milton to make landfall. The presidential action facilitates federal assistance for local authorities.

Unlike Helene, Milton is forecast to sweep northeast across much of Florida before moving into the Atlantic Ocean on Thursday.

It remains "extremely powerful" and "is expected to grow in size and remain an extremely dangerous hurricane when it approaches the west coast of Florida on Wednesday," the National Hurricane Center (NHC) said in an advisory.

"A large area of destructive storm surge, with highest inundations of 10 ft or greater, is expected along a portion of the west-central coast of the Florida Peninsula. If you are in the Storm surge Warning area, this is an extremely life-threatening situation, and you should evacuate today if ordered by local officials," it said.

"There will likely not be enough time to wait to leave on Wednesday," it added.

Milton is expected to remain a hurricane as it makes its way across the Florida peninsula before hitting the Atlantic, bringing with it dauntingly powerful winds and rains that are expected to result in significant flooding. Up to 16 inches (41 cm) of rain is expected in some areas.

A broad band of Florida from Tampa Bay on the west coast to Orlando further east faces a high risk of flash flooding.

The area around Tampa is also expected to receive the highest level of storm surge, or flooding resulting from rising ocean levels. The NHC estimates that waters will rise from 10 to 15 feet (3 to 4.5 meters) in the area.

The agency said that preparations for "long-duration power outages," should be completed by Tuesday night.

The White House earlier announced that Biden was postponing a trip to Germany and Angola that was originally planned to begin this week so that he could oversee the federal response to Milton.

Biden's Oct. 13-15 trip to Angola was to be his first to Africa since he assumed office in 2021, and was expected to fulfill a long-standing promise to visit the continent before he leaves office.

The president maintained that he still plans to go to Angola, and would speak with German Chancellor Olaf Scholz later Tuesday to discuss plans for the trip.

"We've already contacted all these people, okay, but I'm going to be on the phone today," he said.