(Adds latest outages, latest storm track)
Sept 11 (Reuters) - Hurricane Irma knocked out power to about 6.5 million homes and businesses in the U.S. Southeast, mostly in Florida, according to state officials and local electric utilities.
Irma hit southwest Florida on Sunday morning as a dangerous Category 4 hurricane, the second-highest level on the five-step Saffir-Simpson scale. It gradually weakened to a tropical storm by Monday morning as it headed toward Georgia.
The storm, which was moving into southern Georgia, was packing maximum sustained winds of 60 miles (97 km) per hour, according to the U.S. National Hurricane Center's latest update at 2 p.m. EDT (1800 GMT).
Power losses in Georgia, which were nearing 400,000 as of 1 p.m. EDT, were expected to increase as the storm moved north.
In Florida, the state's biggest electric company said its outages had started to decline below the peak of 3.6 million by Monday afternoon. A total of almost 4.5 million Florida Power & Light customers have been affected by the storm, with around 1 million getting service restored, mostly by automated devices.
"We've never had that many outages, and I don't think any utility in the country ever has," FPL Chief Executive Eric Silagy said at a news conference Monday. "It is by far and away the largest in the history of our company."
FPL said it was still assessing the damage and could not yet say when it will restore service to most customers. Some homes and businesses could be without power for weeks, especially in the hardest-hit areas like southwest Florida, the NextEra Energy Inc unit said.
As the storm pushed north, outage figures were increasing at other large utilities, including units of Duke Energy Corp , Southern Co and Emera Inc.
Duke's outages jumped to almost 1.2 million by midday Monday. Emera's Tampa Electric utility reported 332,000 homes and businesses had lost power by Monday afternoon.
FPL said its two nuclear plants were safe. Both units at its Turkey Point facility, located about 30 miles (48 km) south of Miami, were shut by early Monday.
The company closed Turkey Point's Unit 3 on Saturday as Irma approached the coast but decided not shut Unit 4 at that time because the hurricane track shifted away from the plant toward the western part of the Florida Peninsula. FPL, however, shut Unit 4 on Sunday night due to a possible valve issue that was probably not related to Irma, U.S. Nuclear Regulatory Commission officials said on Monday.
At its St. Lucie nuclear plant located about 120 miles (190 km) north of Miami, FPL reduced power at Unit 1 due to salt buildup from Irma in the switchyard, NRC spokesman Roger Hannah said. The plant's other reactor, Unit 2, continued to operate at full power.
Duke's retired Crystal River plant, about 90 miles (145 km) north of Tampa, has spent nuclear fuel, but Hannah said that was not a problem.
As Irma loomed and came ashore, gasoline stations struggled to keep up as people evacuated Florida. In the Atlanta metropolitan area, about 545 stations, or about 13.2 percent of the total, were out of the fuel earlier on Monday, according to information service Gas Buddy.
Irma is expected to sap demand for fuel for a time, Goldman Sachs analysts said in a note on Monday, but they cautioned that supply could remain strained due to refining capacity offline in the wake of Hurricane Harvey, which hit Texas two weeks ago.
(Additional reporting by Timothy Gardner in Washington, DC, Jessica Resnick-Ault in New York and Ruthy Munoz in Houston; Editing by Frances Kerry and Lisa Von Ahn)