Ivan, which has killed 68 people in its deadly trek through the Caribbean over the past 10 days - also triggered devastating tornadoes on Thursday, killing another eight people in the US.
"Devastation. That’s the best description I can give you," said Police Lt Rodney Eagerton in Pensacola, a city of 60,000 in the northwestern corner of Florida.
"We lost all power, water services. We have got numerous trees down. All the traffic lights are down. Roads are washed out, bridges washed out. There is extensive home damage in all areas."
Storm Jeanne, which became a hurricane on 15 September, is expected to travel west to west-northwestward and batter through Florida on its way to the Gulf of Mexico.
Earlier on Thursday, it plowed into the northeastern Dominican Republic, prompting thousands to flee their homes following a punishing passage across Puerto Rico that unleashed floods and killed two people.
Nearly 1.5 million people were without power and thousands huddled in shelters.
Florida has been hit by three
hurricanes in just over a month
At least eight people died in northwest Florida when tornadoes touched down and damaged or destroyed up to 70 buildings, including a fire station.
The dead included an eight-year-old girl when a tree fell on her home.
This was Florida's third hurricane in just over a month. The state was slammed by Hurricane Charley on 13 August and Hurricane Frances on 4 September. The two storms caused a combined damage of $11 billion in insured losses.
But Ivan is the fiercest storm to hit the coast and President George Bush signed declarations making federal disaster assistance available for the battered regions.
"My heart goes out to people who have lost a lot. There is extensive damage and some loss of life," said Florida governor and the brother of the president, Jeb Bush.
Ivan's approach through the Gulf of Mexico disrupted oil and gas production, with closures of offshore oil rigs and refineries on the Gulf Coast.
In Alabama, a quarter of a million people were without power.
New Orleans – the city which was initially feared would take a severe pounding – escaped the storm's path. Tens of thousands of its residents had fled to escape Ivan's wrath.
Fortunately though, the storm's winds have decreased to 120 kph and Ivan was expected to weaken further as it moved over land.
At one point during its Caribbean rampage, Ivan was the sixth most powerful Atlantic hurricane on record, with sustained winds of 265 kph.