With flood levels going past Hurricane Dora's record of 4.1 feet in 1964, Irma dethroned the record-holder after water reached 5.03 feet in Jacksonville, Florida, the National Weather Service reported Monday.
According to Florida's Division of Emergency Management some 5.6 million residents have been ordered to evacuate - almost a quarter of the state population.
However, with more than 6.5 million account holders sitting in the dark, the vast majority of outages are in the Sunshine State, according to Florida Power & Light, Florida's largest electric utility company.
The most powerful Atlantic storm in a decade now has Fort Myers and Naples - and cities as far north as Sarasota and Tampa - square in its sights, forecasters said.
With the arrival of what is potentially one of the most devastating storms to ever hit Florida, officials have set aside 3.2 million liters (0.85 million gallons) of water, filled 67 trailers with meals, and amassed 24,000 tarps. In the Keys, though, he said "there is devastation".
Hurricane Jose remains a unsafe Category 4 storm
There was more good news for the United States, and some of the previously hit Caribbean islands who had been in the path of Irma, but were spared by the second category four Hurricane, Jose. "We don't need any more hurricanes", he said.
"It's frightful, what we saw", Scott said.
He said the water, electricity and sewage systems in the Keys were non-operational, and that trailer parks had been "overturned".
The Keys are linked by 42 bridges that have to be checked for safety before motorists can be allowed in, officials said. "You couldn't get a motel anywhere".
"Irma remains an extremely unsafe hurricane!" tweeted the National Weather Service early today.
The State Department said Monday that US embassies and consulates have reopened in the Dominican Republic, Haiti, the Bahamas, Barbados and Curaçao, although services were limited. About 5,000 of the Keys' 30,000 permanent residents stayed to ride out the storm, Florida Keys spokesman Andy Newman said.
Irma remained 225 miles south of Miami Saturday morning, but the outer bands of the storm have already begun lashing the area with heavy rain and forceful wind gusts.
Motorcycle Rider Killed in No Passing Zone
KHP said the driver of the motorcycle laid it down on the left side in the northbound lane where he was struck by the Malibu. A motorcycle rider from Nebraska was killed in a crash in Northern Kansas on Monday, while passing in a no passing zone.