Tampa, Florida - Storm-battered Florida braced for a direct hit from Hurricane Milton, which strengthened back to a Category 5 storm, as President Joe Biden begged residents to flee what he warned could be the worst natural disaster to hit the state in a century.

As the second huge hurricane in as many weeks rumbled toward Florida's west coast, a sense of looming catastrophe spread as people raced to board up homes and flee.

"It's a matter of life and death, and that's not hyperbole," Biden said from the White House, urging those under orders to leave to "evacuate now, now, now."

Biden's warning came amid a bitter pre-election quarrel, with his Democratic vice president Kamala Harris castigating her rival Donald Trump for peddling false claims that recovery efforts after the first storm, Hurricane Helene, were diverted away from Republicans.

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As of Tuesday, Milton returned to the maximum Category 5 designation, generating maximum sustained winds of 165 mph, the National Hurricane Center said.

"Fluctuations in intensity are likely while Milton moves across the eastern Gulf of Mexico, but Milton is expected to be a dangerous major hurricane when it reaches the west-central coast of Florida Wednesday night," the NHC said.

Governor Ron DeSantis, at a news conference, ticked off town after town and county after county that are in danger.

"Basically the entire peninsula portion of Florida is under some type of either a watch or a warning," he said.

Airlines put on extra flights out of Tampa, Orlando, Fort Myers, and Sarasota, as highways clogged up with escaping traffic and gas stations sold out of fuel.

Hurricane expert Michael Lowry warned that in the Tampa area, home to some three million people, Milton's storm surge "could double the storm surge levels observed two weeks ago during Helene," which brought massive flooding.

Biden postponed a major trip to Germany and Angola to oversee the federal response, as storm relief efforts have emerged as a political battleground ahead of the presidential election on November 5.

Trump has tapped into frustration about the emergency response after Hurricane Helene and fueled it with disinformation, falsely claiming that disaster money had been spent instead on migrants.

Biden on Tuesday slammed Trump's comments as "un-American," while presidential hopeful Harris warned about the danger that misinformation posed to the federal response.

"It's crude. Have you no empathy, man, for the suffering of other people? Have you have no sense of purpose if you purport to be a leader?" she said, challenging Trump directly, during a chat with late night talk show host Stephen Colbert due to be aired later Tuesday.

In a scene of frantic preparation repeated all over Florida, dozens of cars lined up at a sports facility in Tampa to pick up sandbags to protect their homes from flooding.

John Gomez (75) ignored official advice and traveled all the way from Chicago to try to save a second house he has in Florida.

"I think it's better to be here in case something happens," Gomez said as he waited in line.

Scientists say global warming has a role in intense storms as warmer ocean surfaces release more water vapor, providing additional energy for storms, which exacerbates their winds.

The National Oceanic and Atmospheric Administration on Tuesday released footage from a specialist plane called "Miss Piggy" as it flew into the hurricane to collect data.

Paperwork, equipment, and personal items were sent flying as the plane was shaken by wind and rain.

On the ground, communities hit by the deadly Hurricane Helene, which slammed Florida late last month, have rushed to remove debris that could become dangerous projectiles as Milton approaches.

In Mexico's Yucatan, strong winds toppled trees and pylons, and heavy rain caused flooding, but the peninsula avoided major damage or casualties as the storm barreled offshore.

Across the southeastern US, emergency workers are still struggling to provide relief after Helene, which killed at least 230 people across several states.

It hit the Florida coastline on September 26 as a major Category 4 hurricane, causing massive flooding in remote inland towns in states further north, including North Carolina and Tennessee.

Helene was the deadliest natural disaster to hit the US mainland since 2005's Hurricane Katrina, with the death toll still rising.