While the projected track showed Irma raking the state's Gulf Coast, forecasters warned that the entire Florida peninsula - including the Miami metropolitan area of 6 million people - was in extreme danger from the monstrous storm, nearly 400 miles (640 kilometers) wide.
Others chose to stay because they thought the storm would pass on the eastern side of the state.
"We are also praying that it doesn't come our way".
High winds alone could bring down many power lines, she said, and other lines could be damaged by falling trees.
But the county mayor said that number could surge on Thursday depending on the information officials receive from the National Hurricane Center, which is tracking the Category 5 storm.
The storm is on a more western track than earlier in the week and is expected to bring storm surges of up to 8 feet in Tampa and 15 feet in Southwest Florida.
Meanwhile, in Hardee County, sheriff's Deputy Julie Bridges, a 13-year veteran driving home after working at an evacuation shelter, and Sgt. Joseph Ossman, who had been with the Florida Department of Corrections for 21 years, both died in an early morning head-on crash.
"This is a deadly and devastating hurricane, and every part of Florida will feel the wrath of this storm", Silagy said.
Irma made landfall just after 9 a.m.at Cudjoe Key, about 20 miles outside Key West, forecasters said. When that happened, its hurricane-force wind field expanded greatly, to about 110 miles wide, said Jeff Masters, meteorology director at the private service Weather Underground.More news: Florida Sen. Bill Nelson: 'FEMA's going to be stretched' by Irma
One building that did withstand the storm is Ernest Hemingway's former home in Key West, now a museum.
"We could see millions of people without power in Florida for multiple days in some areas, maybe weeks, and so I think it's very important to set the expectations of citizens", Long told CNN's Rene Marsh at his agency's headquarters in Washington on Saturday.
"I don't think anybody alive today in this state has ever seen anything like this", Scott said at the state's emergency operations center when the first parts of the storm started to cross into the Florida Keys.
Six deaths in Florida have been blamed on Irma, along with three in Georgia and one in SC. There were 166,598 customers without power across the state of Georgia, according to Georgia Power.
Tampa Electric told customers on Sunday, however, that response crews were halting work because of the high winds.
He added that Irma could spawn tornadoes and dump as much as 38cm of rain on the peninsula and 63cm on the Florida Keys. Without power, emergency officials are using a backup radio system to communicate, he said. No injuries were reported.
Police in Miami-Dade County and Fort Lauderdale reported making 48 arrests for looting.
- Disney World was forced to close, for only the sixth time in its 45-year history.
The monster storm was responsible for at least 10 deaths after it battered the Caribbean Wednesday.
"You can't survive these storm surges", he said. Florida Governor Rick Scott urged the 5.6 million people in the state to leave as soon as possible and said that those who intend to stay would have to do it at their own risk.