In all about 2 million people and businesses had lost power.
The storm is expected to spread to other states, with 540,000 Georgians ordered to leave and states of emergency declared in Alabama, North Carolina, and SC.
A hurricane warning is now in effect in the provinces of Camaguey, Ciego de Avila, Sancti Spiritus, Villa Clara and Matanzas.
"This is going to be a frustrating event".
The size and trajectory of the storm has prompted officials to order evacuations along both coasts of Florida, including some of the state's population centers.
Emergency managers there declared "the Keys are not open for business" and warned that there was no fuel, electricity, running water or cell service and that supplies were low and anxiety high.
Florida Governor Rick Scott said all Floridians should be prepared for possible evacuation, and issued a stark warning to those in threatened areas.
A tower crane collapsed onto a high-rise building under construction in downtown Miami, the city said in a tweet Sunday morning.
The number of canceled flights was as high as 12,500 at one point earlier in the weekend, but now more flights are expected to be affected as the storm moves into Georgia. He told CNN he has homes there and in Houston, which was hit by heavy flooding from Hurricane Harvey two weeks ago.
Forecasters said metro Atlanta could expect peak winds of 30-40 miles per hour (50 to 65 kph) and gusts up to 55 miles per hour (90 kph) on Monday, with a likelihood of falling limbs and trees blocking roadways and snapping power lines. Additionally, Indian-American hoteliers are also giving out unreserved rooms to those who fled Florida.
US Treasury Secretary Steven Mnuchin told an investor conference in NY that the storm would ultimately boost the economy by sparking rebuilding. "We'll have to wait and see" where to go once damage reports come in, Stone said. "As we rebuild, that will help GDP".
"It's the worst storm I've ever seen", said South, the NOAA meteorologist.
A man died in Worth County, Georgia, on Monday while repairing the roof of a shed during sustained winds of 42 miles per hour (67 kph) with gusts up to 70 miles per hour (112 kph), a National Weather Service report said.
Authorities say a Florida man appears to have been electrocuted by a downed power line following Irma.
Officials have declared a flash flood emergency in Charleston, South Carolina.
Jamie Rhome, head of the U.S. National Hurricane Center's storm surge unit, says large hurricanes tend to create greater storm surge over a broader area, and coastal features such as bays can act like funnels and back water up into rivers and canals.