Cherie Jacobs, a spokesperson for Tampa Electric, said earlier on Monday that some 300,000 residences - approximately 40% of their entire customer base - was without power.
While Irma's passage over land will cause the storm to weaken somewhat, Irma's present size and power - it had maximum sustained winds of 110 miles per hour (175 km/) as of 5 p.m. EDT - suggest that the storm will retain hurricane strength until Monday morning "at the earliest", NHC representatives explained in an advisory.
As the storm loomed and came ashore, gasoline stations struggled to keep up as people evacuated Florida.
Irma, which was expected to cause billions of dollars in damage to the third-most-populous U.S. state, it hit just days after the Houston area was deluged by unprecedented flooding from Hurricane Harvey, which dumped more than 127cm of rain in parts of Texas.
As of 3:35 p.m. Sunday, Irma was a Category 3 hurricane with maximum sustained winds of 120 miles an hour.
First Irma slammed into the Florida Keys Sunday morning as a Category 4 hurricane, ripping roofs off of mobile homes and littering roads with debris.
HURRICANE Irma is showing signs of weakening and could be downgraded to a tropical storm on Monday.
The National Weather Service has told TMZ that the surge of water in Miami has gotten as high as 6 feet in some parts.
"Folks, we must take this storm seriously", Alabama Gov. Kay Ivey told a Sunday news conference. With this northerly track, we'll still likely see some impacts here in Mid-Missouri.
Governor Rick Scott said there was serious threat of "significant storm surge flooding" along the entire west coast of Florida. "We just cannot gamble on the wind".
Widespread power outages: Most of the city doesn't have power, officials said. Other people may put out memes on social media that show forecasts that go beyond five days. Here's what you should know. But Florida Power and Light says they're really concerned about some areas where infrastructure is going to be damaged and it might not be so quick.
According to some reports, almost 4 million to 5 million homes and businesses in Florida lost power, and utility officials said it could take weeks to restore electricity to everyone.