Hurricane Irma, one of the most powerful Atlantic storms in a century, drove toward Florida on Friday as it lashed the Caribbean with devastating winds and torrential rain, leaving behind at least 21 deaths and a swath of destruction.
The "extremely dangerous" hurricane was downgraded from a category 5 to a category 4 early on Friday, but it still packed winds as strong as 155 miles per hour, the U.S. National Hurricane Center (NHC) said in an advisory.
The mayor of Miami Beach, Philip Levine, warned anyone who remained in the resort city to comply with a mandatory evacuation order.
"The size of the storm is massive – it's a nuclear hurricane, it has devastating effects," Levine told CNBC's Closing Bell in a phone interview from Mount Sinai Medical Center. He warned that those who stay behind will not have access to emergency services until the storm passes.
"During the storm itself, when the hurricane comes ashore, our first responders will not be going out there," the mayor said. "We're not going to risk their lives. People have been told, they have been mandated, they've been ordered to leave the beach."
Source: U.S. National Hurricane Center
The storm was last spreading westward over portions of Cuba and the central Bahamas, the NHC said.
It was will continue to move near the north coast of Cuba and the central Bahamas on Friday and Saturday before slamming into southern Florida on Sunday.
In Miami, hundreds lined up for bottled water and cars looped around city blocks to get gas on Thursday. Gasoline shortages in the Miami-Fort Lauderdale area worsened on Thursday, with sales up to five times the norm.
In Palm Beach, the waterfront Mar-a-Lago estate owned by U.S. President Donald Trump was ordered evacuated, media said. Trump also owns property on the French side of Saint Martin, an island devastated by the storm.
Dozens of cities and counties in increasingly-northern regions of Florida are issuing mandatory and voluntary evacuations, many of which are already being executed. Some highways have ground to a halt from congestion as evacuees flee the most dangerous hurricane areas.