While the hurricane is forecast to weaken, Irma is still expected to remain powerful as it moves near or along the west coast of Florida, the National Hurricane Center warns.
Packing 210 kilometres per hour (130-mph) winds, Hurricane Irma knocked out electricity to about two million Florida homes and businesses on Sunday. Irma threatened the state's Gulf Coast with potentially catastrophic flooding.
The storm, one of the most powerful ever recorded in the Atlantic, passed over the Florida Keys archipelago off the state's southern tip. Irma was on a course for the state's western coast, which was expecting storm surges – water driven ashore by the winds – of up to 4.6 metres (15 feet), according to the National Hurricane Center (NHC).
NHC said on Sunday while weakening is forecast, Irma is expected to remain a powerful hurricane while it moves near or along the west coast of Florida.
"I am very concerned about the west coast," Florida Governor Rick Scott told Fox News Sunday.
The coastline is home to cities like Tampa and St Petersburg.
Irma on Sunday was set to make landfall in Florida with devastating winds and threatening storm surges after a destructive march up Cuba's northern coast.
This is a life-threatening situation, the NHC said.
Irma comes just days after Hurricane Harvey dumped record-setting rain in Texas.
The leading edge of the immense storm bent palm trees and spit rain across South Florida, knocking out power to more than 170,000 homes and businesses, as the eye approached Key West.
The storm was a Category 4 hurricane about 70 miles (115 km) south-southeast of Key West, Florida, as of 2 am EDT (0600 GMT) on Sunday with maximum sustained winds of 130 mph (210 kph), the NHC said.
A Category 4 storm is the second-highest designation on the Saffir-Simpson scale. Its current trajectory suggests Irma will slam into St Petersburg which has not suffered a major hurricane in nearly a century.
Wind gusts near hurricane force began to batter the Florida Keys late on Saturday, the NHC said.
The NHC put out a hurricane watch and warning for almost all of the state into Georgia and South Carolina - an area where about 20 million people live.
Storm surges pushed by a high tide were forecast to be as high as 15 feet (4.6 m) for low-lying areas along the state's west coast on Sunday, which could produce catastrophic flooding for thousands of homes.
In the Orlando area, Walt Disney World, Universal Studios and Sea World all were closing Saturday.
The Miami, Fort Lauderdale, Tampa and Orlando airports shut down.
TRT World's Giles Gibson reports from Fort Lauderdale, Florida.
Hurricane Irma ripped roofs off houses and flooded hundreds of miles of coastline as it raked Cuba's northern coast after devastating islands the length of the Caribbean in a trail of destruction that has left 22 people dead so far.
In Cuba, the destruction along the north central coast was similar to that suffered by other Caribbean islands over the last week as Irma plowed into Ciego de Avila province.
It was the first time the eye of a Category 5 storm had made landfall in Cuba since 1932, state media said.
At 09:00 am Saturday, the Cuban government issued a hurricane warning across the country, with more than one million people being evacuated from affected regions.
TRT World spoke to journalist Ed Augustin in Havana, Cuba.
As Irma left Cuba late Saturday and directed its force toward Florida, authorities on the island were assessing the damage and warning of staggering damage to keys off the northern coast studded with all-inclusive resorts and cities, as well as farmland in central Cuba.
There were no immediate reports of deaths in Cuba – a country that prides itself on its disaster preparedness – but authorities were trying to restore power, clear roads and warned that people should stay off the streets of Havana because flooding could continue into Monday.
Residents of "the capital should know that the flooding is going to last more than 36 hours, in other words, it is going to persist," Civil Defense Colonel Luis Angel Macareno said late Saturday. He added the waters had reached at about 2,000 feet (600 meters) into Havana.
Tracking models showed Irma would make landfall on the western side of the Florida peninsula and head up the west coast.
Florida Governor Rick Scott had warned residents in the state's evacuation zones Saturday. "This is your last chance to make a good decision."
About 6.4 million people were told to leave.
But because the storm is 350 to 400 miles wide, the entire Florida peninsula was exposed.
More than 2,000 flights in and out of Florida were cancelled on Saturday, according to tracking service FlightAware.com, and ground transport was scrambled by millions fleeing for safety.
In Palm Beach, President Donald Trump's waterfront Mar-a-Lago estate was under evacuation orders.
This is a storm of enormous destructive power, and I ask everyone in the storm’s path to heed ALL instructions from government officials. pic.twitter.com/nJfM2Sdme1— Donald J. Trump (@realDonaldTrump) September 9, 2017
The city of Miami imposed a curfew until 7 am on Sunday and more than 220,000 customers in Florida were without power on Sunday morning, utilities reported.
Amid urgent warnings from state officials to evacuate before it was too late, downtown Miami was all but abandoned on Saturday.
Sheets of rain and wind gusts of more than 50 mph swept through the deserted city of 400,000 people several hours before expected landfall.
The wind sent a construction crane spinning on the roof of the Miami Worldcenter, a billion-dollar mixed-use project near the home of the Miami Heat basketball team and the city's performing arts centre.
The greater Miami area of 6 million people could still get life-threatening hurricane winds and storm surge of 4 to 6 feet, forecasters said.
Irma vs Harvey
Irma killed at least 22 people in the Caribbean and caused one of the largest evacuations in US history.
It was a Category 5 storm, the highest ranking possible when it crashed into Cuba on Saturday morning.
Irma was forecast to dump up to 20 inches (50 cm) of rain over Florida and southeast Georgia through Monday.
It is less than the 50 inches Hurricane Harvey dropped on parts of Texas and Louisiana two weeks ago, killing at least 60 people and causing an estimated $180 billion in property damage.
Irma could cause insurance-related losses of between $15 billion and $50 billion in the United States, catastrophe modelling firm AIR Worldwide said.
But unlike with Harvey, dangerous winds will barely abate once Irma makes landfall on Sunday morning.
"This is a storm of enormous destructive power, and I ask everyone in the storm’s path to heed ALL instructions from government officials," Trump said on Twitter.
The window for people to leave evacuation zones was rapidly closing on Saturday, officials said.
They warned gas stations would soon be without fuel and bridges would be closed in some areas.
Chris Cardona and his wife Laurie left their mobile home near Miami on Thursday to seek refuge with friends near Tampa.
"Not only did we go west, but so did Irma. She's tracking us, that feisty minx," Cardona, 54, said by phone.