Hurricane Irma strengthened to a Category 4 storm early Sunday as it lashed coastal Florida with 210 kph wind and heavy rain ahead of its expected landfall.
Irma is forecast to cross the Florida Keys before tracking up the western coast of the state.
The National Hurricane Center said the storm's projected track has shifted slightly to the west. That path could allow the storm's center to remain over the warm waters of the Gulf of Mexico, allowing it to strengthen more before moving ashore at St. Petersburg, just west of Tampa.
According to the Florida Power and Light website, more than 250,000 homes and businesses are already without electricity.
Florida Governor Rick Scott told Floridians Saturday evening, “We are under a state of emergency,” urging them to leave evacuation zones.
“This is your last chance to make a good decision," he added.
WATCH: Florida Governor: 'The Storm Is Here'
Scott also repeated his call for nurses and emergency workers to volunteer their help in the aftermath of the storm.
More than 75,000 people heeded the governor's advice and checked into some 400 emergency shelters in the state.
Trump: 'Get out of its way
Meanwhile, President Donald Trump and his Cabinet met Saturday at the presidential retreat in Camp David, Maryland, to discuss the hurricane.
Citing the expected impact of Hurricane Irma, which came on the heels of Hurricane Harvey's destruction in Texas just two weeks ago, Trump said he would ask the Republican-controlled Congress to speed up efforts to overhaul the U.S. tax code.
"I think now with what's happened with the hurricane, I'm going to ask for a speed-up. I wanted a speed-up anyway, but now we need it even more so," he told Cabinet members. The White House released a video of his remarks.
He also called Irma a "storm of enormous destructive power" and asked "everyone in the storm path to heed all instructions, get out of its way."
Irma was a Category 5 when it hit Cuba late Friday. Its time over land reduced the storm's strength. It was a downgraded to a Category 3 storm Saturday but regained power as it moved across the warm waters between Cuba and the U.S.
Florida's slender Key islands — with their population of retirees, vacationers and refugees from mainland culture — were under mandatory evacuation orders.
WATCH: Florida Official: Be Prepared, Be Patient, Get to Shelters
For those who resisted the order and planned to ride out the storm on the Keys, "you're on your own," Federal Emergency Management Agency head Brock Long said Saturday.
"There is no safe area within the Keys," Long said. "You put your life in your own hands by not evacuating."
He added, "We are not going to be there right after the storm passes. We need to make sure roadways are clear, we need to get trucks in to get stuff there."
Curfews for Florida
Further inland, some areas were under curfew late Saturday and early Sunday as residents awaited Irma's onset.
In Homestead, Florida, south of Miami, people have been threatened with arrest if they are out after hours without a "valid, emergency purpose," Zachary Good, spokesman for the city, said.
In Miami-Dade County, officials said more people had checked into hurricane shelters than at any other time in the county's history. About 29,000 people were reported to have checked into county-run shelters, along with about 1,000 pets.
But space remained for last-minute decision-makers: As of Saturday afternoon local time, only 16 of 42 shelters were reported full.
Scott asked residents who planned to stay home to have three days' worth of supplies on hand to sustain themselves until emergency help arrived.
In all, Florida asked 5.6 million people — more than one-quarter of the state's population — to evacuate their homes ahead of the storm. Scott told all Floridians to be prepared in case they needed to leave.
Destruction in the Caribbean
At least 25 people have died since the storm began raking its arms over land, starting with the Caribbean island of Barbuda.
The resort island with a population of fewer than 2,000 was devastated. Prime Minister Gaston Browne estimated that 95 percent of Barbuda's buildings had been damaged or destroyed.
Until late Saturday, the island nation was braced for another direct impact, this one from Category 4 Hurricane Jose. By Saturday evening, Jose had skirted the island without imposing a direct hit.
It could be up to six months before all power is restored on cash-strapped Puerto Rico, a U.S. commonwealth, where Irma knocked out power to more than 1 million people.
The U.S. Defense Department deployed three Navy ships, about two dozen aircraft and hundreds of Marines to help with recovery efforts in Puerto Rico and the U.S. Virgin Islands.
VOA Turkish service's Mehmet Sumer contributed to this report.