(Adds latest outages, Florida nuclear plant updates)
Sept 11 (Reuters) - Hurricane Irma knocked out power to about 5.8 million homes and businesses in Florida, even as the storm weakened 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 hurricane, the second-highest level on the five-step Saffir-Simpson scale. It gradually lost strength and weakened to a tropical storm by Monday morning as it headed toward Georgia, the U.S. National Hurricane Center said at 8 a.m. EDT (1200 GMT)..
Maximum sustained winds were at 70 miles (110 km) per hour, the forecaster said.
Power losses in Georgia, which were at about 152,000 as of 8:45 a.m. EDT, were expected to increase as the storm moved north.
In Florida, the state's biggest electric company said its outages came to more than 3.6 million by 8:30 a.m. on Monday. A total of 4.2 million Florida Power & Light customers have been affected, with about 570,000 getting service restored, mostly by automated devices.
Full restoration of power could take weeks in many areas due to expected damage to FPL's system, 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 more than 860,000 overnight; the company said they could ultimately exceed 1 million. Emera's Tampa Electric utility reported 300,000 homes and businesses lost power by Monday morning.
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 started to reduce 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 the storm loomed and came ashore, gasoline stations struggled to keep up as people evacuated Florida. In the Atlanta metropolitan area, about 13.2 percent of stations were out of the fuel, 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.
(Reporting by Scott DiSavino and Jessica Resnick-Ault in New York; Additional reporting by Ruthy Munoz in Houston; Editing by Frances Kerry and Lisa Von Ahn)