MIAMI -- After battering Cuba early Saturday and leaving more than 20 dead across the Caribbean, a dangerous Hurricane Irma is taking aim at south Florida with winds nearing 125 mph as another hurricane follows close behind.

Irma regained Category 5 status overnight, then dropped back to Category 3 on Saturday as thousands of people in the Caribbean fought desperately to find shelter or escape their storm-blasted islands. Nearly 7 million people in Florida and Georgia were warned to leave their homes as the storm was forecast to regain strength before slamming the U.S.

As of 2 p.m. Saturday, Irma was about 125 miles southeast of Key West, according to the National Hurricane Center (NHC).

The storm made landfall in Cuba's Sabana-Camagüey archipelago, north of the eastern Camaguey province, CBS News' Portia Siegelbaum reports. Puerto Padre, located along the northern coast of Ciego de Avila province and just west of Camaguey, lost electricity a short while ago as the town is taking a beating from the outer bands of Irma. Rain and wind brought down trees and street lights.

Get Breaking News Delivered to Your Inbox

Cuba's hurricane expert Jose Rubiera urged everyone to carefully monitor Irma, Siegelbaum reports. He warned that it's an extremely powerful, extremely large storm and said that when Irma finally turns north, strong tropical storm wind and rain will slam the capital Havana and the neighboring western provinces of Mayabeque and Pinar del Rio.

The NHC said Saturday morning that the storm had weakened over Cuba. The center says the center of the storm is expected to turn north sometime late Saturday and arrive in the Florida Keys Sunday morning.

Hurricane Irma made landfall on the northern coast of Cuba on Sept. 8. NASA Earth

The National Weather Service in Key West said wind gusts of 66 mph were recorded early Saturday.

A @FlKeysMosquito sensor on Lower Matecumbe Key recently recorded a wind gust of 66 mph (57 knots). #Irma #FLwx #FLKeys — NWS Key West (@NWSKeyWest) September 9, 2017

The NHC also increased the storm surge warning northward on both the east and west coasts of Florida.

In one of the country's largest evacuations, about 6.3 million people in Florida -- more than one-quarter of the state's population -- were ordered to leave, and another 540,000 were ordered out on the Georgia coast. Authorities opened hundreds of shelters for people who did not leave. Hotels as far away as Atlanta filled up with evacuees.

Forecasters adjusted the storm's potential track more toward the west coast of Florida, away from the Miami metropolitan area of 6 million people, meaning "a less costly, a less deadly storm," University of Miami researcher Brian McNoldy said.

Nevertheless, forecasters warned that its hurricane-force winds were so wide they could reach from coast to coast, testing the nation's third-largest state, which has undergone rapid development and more stringent hurricane-proof building codes in the last decade or so.

"This is a storm that will kill you if you don't get out of the way," National Hurricane Center meteorologist Dennis Feltgen said. "Everybody's going to feel this one."

The National Hurricane Center's forecast cone as of 5 a.m. Saturday. National Hurricane Center

Irma killed at least 20 people in the Caribbean and left thousands homeless as it devastated small resort islands known for their turquoise waters and lush green vegetation

Puerto Rico, the Dominican Republic and the eastern part of Cuba reported no major casualties or damage by mid-afternoon after Irma rolled north of the Caribbean's biggest islands.

But many others residents and tourists farther east were left reeling after the storm ravaged some of the world's most exclusive tropical playgrounds. Among them: St. Martin, St. Barts, St. Thomas, Barbuda and Anguilla.

Irma smashed homes, shops, roads and schools; knocked out power, water and telephone service; trapped thousands of tourists; and stripped trees of their leaves, leaving an eerie, blasted-looking landscape littered with sheet metal and splintered lumber.

On Friday, looting and gunshots were reported on St. Martin, and a curfew was imposed in the U.S. Virgin Islands.

Many of Irma's victims fled their islands on ferries and fishing boats for fear of Hurricane Jose, a Category 4 storm with 145 mph winds that could punish some places all over again over the weekend.

"I don't think it takes a rocket scientist to know that further damage is imminent," said Inspector Frankie Thomas of the Royal Police Force of Antigua and Barbuda.

In Florida, gas shortages and gridlock plagued the evacuations, turning normally simple trips into tests of will. Parts of interstates 75 and 95 north were bumper-to-bumper, while very few cars drove on the southbound lanes.

"We're getting out of this state," said Manny Zuniga, who left his home in Miami at midnight Thursday to avoid the gridlock. "Irma is going to take all of Florida."

Despite driving overnight, he still took 12 hours to reach Orlando -- a trip that normally takes four hours. From there, he and his wife, two children, two dogs and a ferret were headed to Arkansas.

Emergency officials in the Keys told Gov. Rick Scott that first responders will evacuate Saturday morning, CBS Miami reports.

"Once a dangerous storm starts, don't dial 911 during it because nobody is going to answer," Monroe County Administrator Roman Gastesi told the station.

Scott has ordered all Florida public schools statewide to close so the buildings can be used as shelters. He urged resident Friday not to be complacent.

"Think about your life, think about your family's life. But five to 10 feet of storm surge in the southern part of the state -- think about that. That's going to cover homes. We're not a high state. We don't have mountains in the state," Scott said on "CBS This Morning."

Brian McNoldy, a hurricane researcher at the University of Miami, said Irma could easily prove to be the costliest storm in U.S. history.

Tony Marcellus racked his brain to figure out a way to get his 67-year-old mother and 85-year-old grandfather out of their home five blocks from the ocean in West Palm Beach. He lives 600 miles away in Atlanta. He checked flights but found nothing and rental cars were sold out, so he settled on a modern method of evacuation.

He hired an Uber to pick them up and drive them 170 miles to Orlando, where he met them to take them to Atlanta. He gave the driver a nice tip.

"I have peace of mind now," said Marcellus' mother, Celine Jean. "I've been worried sick for days."

Several small, poor communities around Lake Okeechobee in the south-central part of Florida were added to the evacuation list because the lake may overflow - but the governor said engineers expect the protective dike to hold up. Many people in the area said they wouldn't leave because they either had no transportation or nowhere to go.

Disney World parks will close early Saturday and remain shuttered through Monday, as will Universal Orlando and SeaWorld.

Miami-Dade County Mayor Carlos Gimenez said he planned for enough space to hold 100,000 people before the storm arrives, although most shelters were only beginning to fill on Friday.

Hurricane Andrew in 1992 revealed how lax building codes had become in the country's most storm-prone state, and Florida began requiring sturdier construction. Now, experts say a monstrously strong Irma could become the most serious test of Florida's storm-worthiness since then.

Andrew razed Miami's suburbs with winds topping 165 mph, damaging or blowing apart over 125,000 homes. Almost all mobile homes in its path were obliterated. The damage totaled $26 billion in Florida's most-populous areas. At least 40 people were killed in Florida.

CoreLogic, a consultant to insurers, estimated that nearly 8.5 million Florida homes or commercial properties were at extreme, very high or high risk of wind damage from Irma.

Police in the Fort Lauderdale suburb of Davie said a 57-year-old man who had been hired to install hurricane shutters Thursday morning died after falling about 15 feet from a ladder and hitting his head on a pool deck. The man's name wasn't immediately released.

Forecasters predicted a storm surge of 6 to 12 feet above ground level along Florida's southwest coast and in the Keys. As much as a foot of rain could fall across the state, with isolated spots receiving 20 inches.

With winds that peaked at 185 mph, Irma was once the most powerful hurricane ever recorded in the open Atlantic.