Hurricane Irma, the most powerful Atlantic storm in a decade, hit Cuba overnight as a rare Category 5 storm before being downgraded to a Category 3 Saturday morning. It is expected to strengthen again as it heads toward Florida.

Irma as of about noon Saturday was near the north coast of Cuba and 175 miles southeast of Key West with winds of 125 mph. It was moving west at 9 mph and is expected to turn north and head up the western coast of Florida, making landfall from early Sunday to early Monday as far north as Tampa.

“This is a life-threatening situation,” Florida Gov. Rick Scott said Saturday. “Our state has never seen anything like it.”

The governor stressed the dangers of what he called a “deadly, deadly, deadly storm surge.”

ABC News meteorologists are forecasting storm surges of 10 feet in Tampa and Sarasota, and 10 to 15 feet from Fort Myers to Naples. Somewhat lower storm surges of 3 to 6 feet may occur from Miami to Key Largo.

Winds were already picking up in Florida early Saturday, with gusts between 40 and 60 mph.

Power outages, halted flights and empty ATMs in Florida

Florida’s governor said 25,000 power outages were reported as of Saturday morning.

The state’s residents should anticipate days-long power outages, FEMA said.

Ahead of Irma’s arrival in the Sunshine State, the last flights departed Friday night from Miami International Airport and Fort Lauderdale-Hollywood International Airport. Miami’s airport officially remains open, while Fort Lauderdale’s airport is closed for Saturday and Sunday.

Many ATM machines across southwest Florida were out of cash by late Friday night after people stocked up in case Hurricane Irma causes power outages that make debit and credit card transactions impossible, The Associated Press reported.

‘Extremely dangerous’

“This is as real as it gets,” the National Weather Service in Key West tweeted Friday evening.

The National Hurricane Center on Friday cautioned that Irma’s winds would likely be strong enough to uproot trees, bring down power poles and rip off the roofs and some exterior walls of well-built frame homes.

“Obviously Hurricane Irma continues to be a threat that is going to devastate the United States,” Brock Long, administrator of the Federal Emergency Management Agency (FEMA), said at a press conference Friday morning. “We’re going to have a couple rough days.”

Millions evacuate; many others take shelter

Approximately 6.3 million Floridians are under mandatory or voluntary evacuations, the Florida Division of Emergency Management said Saturday. When evacuation orders in South Carolina and Georgia are included, the number climbs to 6.8 million.

Georgia Gov. Nathan Deal declared a state of emergency for 94 counties in his state, and South Carolina Gov. Henry McMaster issued mandatory evacuations for barrier islands in Colleton, Beaufort and Jasper.

Scott said Saturday that 320 shelters were already open across Florida. Scott said 54,000 Floridians have taken shelter and there is room for more.

Miami-Dade County Mayor Carlos A. Giménez said Saturday morning about 25,000 residents are sheltered in Miami-Dade alone, a number he called “unprecedented in our history.”

“We must remain vigilant,” Giménez said. “The storm will still strengthen … and we will be impacted.”

Palm Beach County has issued a curfew to prevent looting and other criminal activity as the storm approaches, according to a press release. The curfew goes into effect Saturday at 3 p.m. It is unclear when it will be lifted. Broward County set a curfew for 4 p.m. Saturday and in Broward County no unauthorized vehicles will be allowed on the roads.

Irma turns to U.S. after pummeling the Caribbean leaving at least 20 dead

At least 20 people have died and thousands were left homeless after Irma battered a string of Caribbean islands on Wednesday, according to the AP. At the time, Irma was a Category 5 hurricane with maximum sustained winds of 185 mph.

At least three people died from the storm in the U.S. territory of Puerto Rico.

The Turks and Caicos islands were hit hard as Irma passed over the tiny archipelago in the Atlantic Ocean. A government spokesperson told ABC News the British overseas territory had sustained “catastrophic” damage.

The National Hurricane Center warned of a storm surge up to 20 feet on Turks and Caicos with 8 to 12 inches of rain for the low-lying islands through Sunday.

Long, the FEMA administrator, said Friday that the agency’s primary goal is to “stabilize the Virgin Islands and Puerto Rico” by restoring power, maintaining security and bringing in life-sustaining supplies.

ABC News’ Daniel Peck and Max Golembo contributed to this report.