Hurricane Irma, which has toppled cranes, swallowed streets and left millions without power, weakened to a Category 1 storm Monday but remained dangerous as it continued its furious climb up Florida's southwest coast.
Warnings of hazardous storm surges remained in effect through vast swaths of peninsular Florida, where more than six million people had been ordered to flee Irma's path -- one of the biggest evacuations in US history.
"As little as six inches of moving water can knock you down," tweeted the state's governor Rick Scott following the downgrade.
"Stay inside. Stay safe," he added.
Maximum sustained winds had decreased to 85 miles per hour as of 2:00 am local time (0600 GMT), with Irma projected to become a tropical storm as it moved into northern Florida or southern Georgia later Monday.
After wreaking a trail of death and destruction through the Caribbean, Irma had killed three people when it struck the southern Florida Keys island chain as a more powerful Category Four on Sunday.
More than four million customers were without power throughout the state, according to Florida's Division of Emergency Management. Florida Power and Light said it had "safely shut down" one of two nuclear reactors at its Turkey Point power plant.
Handfuls of holdout residents, having defied calls to evacuate, hunkered down as Irma tore over the Keys, ripping boats from their moorings, flattening palm trees and downing power lines across the island chain popular for fishing and scuba diving.
Hours later, one of the mightiest hurricanes ever to slam the state made a second landfall on Marco Island near the beach resort of Naples.
"I am concerned about people that don't believe in the storm surge," said Virginia Defreeuw, 76, who fled her mobile home in Naples to a shelter. "You need to be afraid of the storm surge! People are not listening."
As Irma appeared to set its sights on the Tampa area -- home to three million residents, about half of whom live less than 10 feet above sea level -- some people were taken by surprise by Irma's northwest shift.
Facing Irma's wrath, Tampa Mayor Bob Buckhorn said the city did everything it could to get people out of the coastal areas.
"I am sure there are still people that are still there, thinking that they can hunker down on this storm," Tampa Mayor Bob Buckhorn told a press briefing Sunday, before paraphrasing a famous boxer's words.
"I never thought I would be quoting Mike Tyson, but 'Everybody has a plan until they get punched in the face,'" he said.
"Well, we are about to get punched in the face."
While southwest Florida bore the deadly brunt of Irma's wrath Sunday, the coastlines of Miami and the neighboring island of Miami Beach were heavily inundated by storm surges as hurricane winds sent two giant construction cranes crashing down.
The sea swallowed the coastal walkway of glitzy Brickell Avenue in the center of Miami, flooding the streets and leaving cars half-submerged.
"The wooden pier is basically gone," said Steven Schlacknam, a 51-year-old visual artist watching from a 37th floor apartment.
President Donald Trump, who vowed to travel to Florida "very soon," approved the state's request for emergency federal aid to help with temporary housing, home repairs, emergency work and hazard mitigation.
"Right now, we're worried about lives, not cost," Trump said.
At least 30 deaths are already attributable to the storm. The US victims included a sheriff's deputy killed in a head-on collision early Sunday as she drove home for supplies after working in a shelter all night.
Irma smacked the Keys 57 years to the day after Hurricane Donna hit the same area in 1960, destroying nearly 75 percent of the island chain's buildings.
A shelter of last resort set up in the Middle Keys city of Marathon was reported to be without power or running water, and surrounded by surging waters.
Irma also led to some uniquely Floridian responses, with a sheriff forced to warn residents not to shoot at the storm after an online prank promoting the idea went viral.
"To clarify, DO NOT shoot weapons @ #Irma," the office of the sheriff of Pasco County, on the state's west coast, tweeted hours before landfall.
In Miami, where emergency services were sheltering in place, a dispatcher talked a woman through delivering her own baby on Sunday morning, Assistant Fire Chief Eloy Garcia told the Miami Herald.
Before reaching the United States, Irma smashed through a string of Caribbean islands from tiny Barbuda on Wednesday, to the tropical paradises of Saint Barthelemy and Saint Martin, the US Virgin Islands, Puerto Rico, the Dominican Republic, Haiti and the Turks and Caicos.
Terrified Cubans who rode out Irma in coastal towns -- after it made landfall Friday on the Camaguey archipelago as a maximum-strength Category Five storm -- reported "deafening" winds, uprooted trees and power lines, and rooftops blown off.
There were no immediate reports of casualties in Cuba but it caused significant damage, and enormous waves lashed the Malecon, Havana's emblematic seafront, with seawaters penetrating deep into the capital.
Residents in the old colonial city were waist-deep in floodwaters after Irma cut power and forced the evacuation of more than a million people.
Irma is so wide that both coasts of Florida and the Keys faced destructive storm surges as the storm barreled north.
Businesses on both Florida coasts were shuttered while Miami airport was closed and not expected to reopen until Tuesday.
MacDill Air Force Base in Tampa, the military installation home to US Central Command, issued mandatory evacuation orders ahead of the storm's passage early Monday, while the Kennedy Space Center on the east coast was also closed.