More than a million people in the path of Hurricane Milton have been warned to evacuate or “you’re going to die” as the monster storm intensifies and could be the worst to hit Florida in a century.

Milton is the second dangerous hurricane to hit the US state in less than two weeks and is barrelling towards Tampa Bay, home to more than three million people.

A Hurricane hunter plane flying in the eye of the storm found Milton was strengthening again after weakening slightly from a category five to a still-powerful top-end category four.

Wind speeds of 250km/h were recorded and the US National Hurricane Centre expected Milton to remain an “extremely dangerous hurricane” and potentially re-intensify as it approached land.

Tampa Bay Mayor Jane Castor told CNN that anyone who ignored warnings to leave at-risk areas was dicing with death because the storm surge “was not survivable”.

”I can say without any dramatisation whatsoever. If you choose to stay in one of those evacuation areas, you’re going to die,” she said on Tuesday (local time).

“This is something that I have never seen in my life.

“I can tell you that anyone who was born and raised in the Tampa Bay area has never seen anything like this before. People need to get out.”

Almost all of Florida’s west coast is under a hurricane or tropical storm warning, with Milton spinning just off Mexico’s Yucatan peninsula and edging towards the state.

Authorities have ordered evacuations for areas adjacent to Tampa Bay, encompassing one million residents.

“You do not have to get on the interstate and go far away,” Governor Ron DeSantis said, assuring residents there would be enough petrol to fuel their cars for the trip.

“You can evacuate tens of miles; you do not have to evacuate hundreds of miles away. You do have options.”

Drivers waiting in a long line for fuel early on Tuesday (local time) said they had no plans to evacuate.

“I think we’ll just hang, you know, tough it out,” Martin Oakes, of Apollo Beach, said.

“We got shutters up; the house is all ready. So this is sort of the last piece of the puzzle.”

The densely populated west coast of Florida, still reeling from the devastating Hurricane Helene less than two weeks ago, is bracing for the storm to cross the coast on Wednesday (local time).

‘Worst in 100 years’

President Joe Biden said Milton could be “one of the worst storms” to hit Florida in a century.

“I’ve been briefed by senior leaders of this administration, and we’re driving up preparedness for Hurricane Milton, which could be one of the worst storms in 100 years in Florida,” he said from the White House.

“If you’re under evacuation orders, you should evacuate now, now, now.

“You should have already evacuated. It’s a matter of life and death and that’s not hyperbole.”

Fed by warm waters in the Gulf of Mexico, Milton became the third-fastest intensifying storm on record in the Atlantic Ocean, the hurricane centre said.

It surged from a tropical storm to a category-five hurricane in less than 24 hours.

Its path from west to east was also unusual, as Gulf hurricanes typically form in the Caribbean Sea and make landfall after travelling west and turning north.

“It is exceedingly rare for a hurricane to form in the western Gulf, track eastward, and make landfall on the western coast of Florida,” said Jonathan Lin, an atmospheric scientist at Cornell University.

“This has big implications since the track of the storm plays a role in determining where the storm surge will be the largest.”

The hurricane centre forecast storm surges up to 4½ metres along a stretch of coastline north and south of Tampa Bay.

Hurricane centre deputy director Jamie Rhome said Milton was expected to expand before crossing the coast on Wednesday, putting hundreds of kilometres of coastline within the storm surge danger zone.

Milton was likely to remain a hurricane throughout its journey across the Florida peninsula, Rhome said.

With one last day for people to evacuate on Tuesday, local officials raised concerns of traffic jams and long lines at petrol stations.

Relief efforts remain ongoing throughout much of the US south-east after Helene, a category-four hurricane hit Florida on September 26. It killed more than 200 people and caused billions of dollars in damage across six states.

-with AAP