Irma hit Florida on Sunday morning as a dangerous Category 4 storm, the second-highest level on the five-step Saffir-Simpson scale.
Hurricane Irma knocked out power to about 5.8 million homes and businesses in Florida, even as the storm's power waned as it crept up the state's west coast, according to state officials and local electric utilities.
Irma hit Florida on Sunday morning as a dangerous Category 4 storm, the second-highest level on the five-step Saffir-Simpson scale. The storm gradually lost strength, weakening to a Category 1 hurricane by Monday morning. At 5 a.m. ET, Irma was carrying maximum sustained winds of nearly 75 mph, the National Hurricane Center said.
Most of the power losses were in Florida, but losses in Georgia, which were at about 90,000 as of 6 a.m. ET, were expected to increase as the storm moved north.
FPL, the biggest power company in Florida, said more than 3.6 million of its customers were without power by 6 a.m. A total of 4.2 million have been affected, with about 570,000 seeing service restored, mostly by automated devices.
Full restoration of power could take weeks in many areas, FPL said, because of expected damage to the company's system. FPL is a unit of the Florida energy company NextEra Energy Inc.
Other large utilities, including units of Duke Energy Corp., Southern Co., and Emera Inc., were seeing their figures grow as the storm pushed north.
Duke's outages jumped to 860,000 overnight; the company said it expected outages could ultimately exceed 1 million. Emera's Tampa Electric utility reported that 300,000 homes and businesses lost power by Monday morning.
FPL said its two nuclear plants were safe. It shut only one of the two reactors at its Turkey Point nuclear plant about 30 miles south of Miami on Saturday, rather than both, because the storm shifted track. It left reactors in service at the St. Lucie plant about 120 miles north of Miami.
There is also spent nuclear fuel at Duke's Crystal River plant, about 90 miles north of Tampa. The plant stopped operating in 2009 and was retired in 2013.
In a worst-case scenario, the spent fuel could release radiation if exposed to the air, but Scott Burnell of the US Nuclear Regulatory Commission said that was extremely unlikely.
As the storm loomed and came ashore, gasoline stations struggled to keep up. In the Atlanta metro area, about 496 stations, or 12.2%, were out of gasoline, according to the information service Gas Buddy.
Irma is expected to sap demand for fuel for a time, analysts at Goldman Sachs said in a note Monday, though they cautioned that supply could remain strained because of limits to refining capacity caused by Hurricane Harvey, which hit Texas two weeks ago.
(Reporting by Scott DiSavino and Jessica Resnick-Ault in New York, Additional reporting by Ruthy Munoz in Houston; Editing by Sandra Maler, Peter Cooney and Frances Kerry)