The company has restored power to about 1 million customers so far but CEO Eric Silagy said Monday that "even though we are restoring power, people need to be prepared for some prolonged and extended outages".
Irma hit Florida on Sunday morning as a risky Category 4 storm, the second highest level on the five-step Saffir-Simpson scale.
- 5.8 million customers are without power across Florida, state emergency officials said.
The monster storm, which arrived in Florida as a Category 4 hurricane, has toppled at least three constructions cranes - two over downtown Miami and one in Fort Lauderdale.
Other areas of the state, however, remain largely incapacitated, including the Florida Keys, where an estimated quarter of the homes were destroyed. They worked with the residents to cut a hole in the second story of the home to enter and survive the six-foot-high storm surge. Savannah, Georgia, has also been seeing flooding as Irma's winds push Atlantic waters toward the coast. Reports say that 10,000 people made a decision to ride out the storm.
Both Florida senators got an aerial view of the Keys Monday, where the full extent of the damage still isn't known because some of the islands aren't easily accessible.
A tornado spun off by Irma was reported on the Georgia coast, and firefighters inland had to rescue several people after trees fell on their homes. From Georgia to SC, the storm left behind massive flooding and destruction.
The first sign of daylight is a chance for families on Marco Island to see what Hurricane Irma did to their paradise.
Local, state and federal authorities are coordinating airborne relief efforts to bring supplies to residents who didn't evacuate the Keys, Monroe County Administrator Roman Gastes told CBS Miami.
"We are finding some remains", she said in an interview with CNN.
Georgia Gov. Nathan Deal has already declared a state emergency for all 159 counties as Irma barrels toward the state.
Six deaths in Florida have been blamed on Irma, along with three in Georgia and one in SC.
State government offices are closed, as are public schools and state college and universities.
Last month, Hurricane Harvey devastated much of coastal Texas and killed more than 70 people.