Hurricane Irma continues to hurtle toward Florida’s doorstep, threatening to ravage the state with destruction not seen in a generation.

As the weather forecasts and warnings from officials grew increasingly dire, hundreds of thousands of people across Florida fled their homes before the rapidly closing window to escape Irma’s wrath slammed shut. Forecasters said Irma, a hurricane of remarkable size and power that already has battered islands across the Caribbean, would approach South Florida by Sunday morning and is likely to slam into its southern tip before tracking north across a heavily populated area.

“It’s not a question of if Florida’s going to be impacted, it’s a question of how bad Florida’s going to be impacted,” William “Brock” Long, administrator of the Federal Emergency Management Agency, said Friday at a news conference.

Officials in Georgia and the Carolinas where heavy rains and flooding are expected early next week have declared emergencies, but attention remained focused on Florida. Forecasts call for up to 20 inches of rain and thrashing winds no matter how the storm pivots before hitting the mainland United States.

“Irma is likely to make landfall in Florida as a dangerous major hurricane, and will bring life-threatening wind impacts to much of the state regardless of the exact track of the center,” the National Hurricane Center said.

As of 5 a.m. Saturday, Irma had maximum sustained winds near 155 mph and higher gusts as it moved over Cuba’s Camaguey Archipelago as a Category 4 storm, the hurricane center said.

Local, state and federal officials have offered ominous warnings as the storm zeroed in on Florida, making clear how much danger they felt the Sunshine State could face in coming days. Long urged people from Alabama to North Carolina to monitor and prepare for the storm, calling it “a threat that is going to devastate the United States, either Florida or some of the southeastern states.”

Floridians are familiar with ominous forecasts and hurricane warnings, and many have painful memories of Hurricane Andrew, which made landfall as a Category 5 monster in 1992, and other storms that brought lashing rain and winds. But when asked about people in South Florida who intend to ride out the storm at home, Long was blunt.

“I can guarantee you that I don’t know anybody in Florida that’s ever experienced what’s about to hit South Florida,” Long said. “They need to get out and listen and heed the warnings.”

Mark DeMaria, acting deputy director of the hurricane center, said Friday afternoon that the latest models showed the storm track shifting slightly to the west, putting southwest Florida in particular jeopardy for the most violent winds, while all of South Florida will have significant impacts.

“We really want to emphasize the very vulnerable Southwest Florida area,” DeMaria said.

Florida Gov. Rick Scott (R) has warned people that evacuation zones could expand and said that all Floridians “should be prepared” to leave their homes. Scott also has cited the memories of Andrew, calling Irma “more devastating on its current path” and warning that much of the state could be imperiled.

In addition to having intense power, Irma also is an immense storm, with forecasters reporting hurricane-force winds extending some 70 miles from the center and tropical-storm-force winds extending as far as 195 miles out.

Airports around the state said they would suspend flights and cease operations. Publix, a grocery-store chain, announced plans to close stores across the state in waves and did not say when they would reopen. Tom Bossert, homeland security adviser to President Trump, on Friday said that people need to have enough food and water to get by during a period when the rain and wind will prevent authorities from getting to them.

“We have pre-deployed and pre-staged, but we can’t actually get to that final point of care until conditions permit,” he said Friday during a White House briefing.

The National Hurricane Center has issued a hurricane warning covering all of South Florida, where local officials have ordered evacuations along the coast. In Miami-Dade County, the state’s most populous, mandatory evacuations were issued for about 660,000 people, including for Miami Beach and Key Biscayne. It was the largest evacuation ordered in Miami-Dade history, said Carlos A. Gimenez, the county’s mayor.