The storm was 400 miles wide when it blew ashore Sunday.
St. Petersburg-based Duke Energy, with almost 1.8 customer accounts, was working to restore power to 1.2 million customers. It gradually weakened as it headed through the state, becoming a tropical storm and then a tropical depression on Monday.
Hurricane Irma's powerful center crossed the Florida Keys and tore into the state's Gulf Coast, downing trees, hurling street signs and debris, and knocking the power out to hundreds of thousands of residents throughout the state.
As the hurricane moves north and the wind directions change, the water will start to rush back in and storm surge flooding will occur.
Irma's heavy rain could also bring flash flooding and rapid rises on creeks, streams and rivers.
Scott says the Navy has deployed the USS Iwo Jima, USS New York and the aircraft carrier Abraham Lincoln to help with search and rescue amid reports of devastation in the hurricane-battered Keys.
At 9 a.m., more than 200,000 people were in 587 shelters across the state.
"I just hope everybody survived", Scott said after flying over the archipelago Monday.
The storm killed at least 28 people as it raged westward through the Caribbean on the way to Florida, devastating several small islands, and grazing Puerto Rico, the Dominican Republic and Haiti before pummelling parts of Cuba's north coast with 11m waves.
Anxious relatives, generous volunteers and frantic neighbors turned to social media after Hurricane Irma wiped out electricity and cell service to many communities around Florida, cutting off most contact with remote islands in the Keys.
Hours later, one of the mightiest hurricanes ever to slam the state made a second landfall on Marco Island near the beach resort of Naples.
The major theme parks of Disney World, Universal and SeaWorld are all going to try to open on Tuesday.
Ocean waters also receded in Tampa, as the area on Florida's west coast waited for the worst of the storm to arrive. SeaWorld reported that all its animals and personnel were safe.