Florida Power & Light, the state's largest electric utility, said there were almost 1 million customers without power in Miami-Dade County alone.
Boston: Hurricane Irma smashed into Florida as a powerful Category 4 storm, driving a wall of water and violent winds ashore and marking the first time since 1964 the USA was hit by back-to-back major hurricanes.
At 5 p.m. ET, the storm was about 5 miles north of Naples, Florida, packing maximum sustained winds of 110 mph.
Officials reported four storm-related deaths and urged Floridians to stay off the roads.
At least 25 people died when Irma earlier hit several Caribbean islands.
PARADISE may be lost for now but the devastated islands of the Caribbean hit by the full force of Hurricane Irma will recover.
Antigua and Barbuda were spared from the worst of Jose, as it skirted north of the island on Saturday and was downgraded to a tropical storm warning.
The eye of the hurricane was 20 miles east-southeast of Key West as of 8 am local time (1200 GMT), threatening risky storm surges up to 4.5 meters - enough to cover a house.
"Sheets of zinc that came flying into our backyard also damaged the kitchen wall and we lost many roof tiles", said Angel Coya, 52, adding he was optimistic that Cuba's Communist government would help fix the damage. Petersburg area, though in a weakened state.
Expected to be even more risky than the powerful winds are the storm surges that threaten Florida's coastal cities.
One of the mightiest hurricanes ever to slam storm-prone Florida, Irma is threatening risky storm surges of up to 15 feet (4.5 meters), enough to cover a house, as it collides with the state after sowing devastation through the Caribbean.
"These winds are stronger than those of Kate", said Rosa, referring to the devastation wrought in 1985 by Hurricane Kate.
In Key West, police opened a "shelter of last resort" for those who had ignored evacuation orders.
On Wednesday, the fierce storm hit the northeastern Caribbean islands with 185 miles per hour winds, moving through Barbuda and St. Martin. "You are running out of time to make a decision", Scott said.
The wind sent a construction crane spinning on the roof of the Miami Worldcentre, a billion dollar mixed-use project near the home of the Miami Heat basketball team and the city's performing arts centre.
Florida Power and Light estimated 3.4 million of its customers could be without power at some point during Irma, the company's largest number of outages ever.
"I just spoke to Anaida, it is hard to believe she is getting ready to go through the same thing I just did", she said.
Debris strewn across a normally busy street in South Beach as Hurricane Irma passes by, Sunday, Sept. 10, in Miami Beach, Florida.
The U.S. State Department helped more than 500 Americans fly out of St. Martin, starting with those in need of urgent medical care, spokeswoman Heather Nauert said.
The National Hurricane Center forecast that its center eye will move near or over the state's west coast later on Sunday.