(Adds latest outage numbers, other utilities, Crystal River nuclear plant)
Sept 10 (Reuters) - More than 1.6 million homes and businesses in south Florida were without power from Hurricane Irma on Sunday, the state's largest utility said, and repairs to its system will take weeks, threatening to leave millions in the dark.
Much of the state has not yet felt the full brunt of the storm as Irma barreled across the Florida Keys on Sunday morning and headed for the state's southwest coast with maximum sustained winds of 130 miles (215 kilometers) per hour, making it a Category 4 storm, the second worst on the Saffir-Simpson scale.
In all, almost 1.8 million FPL homes and businesses had lost power. At 1 p.m. EDT (1700 GMT), nearly 1.6 million were without power while about 200,000 had electricity restored mostly by automated devices, FPL said.
"We will have to rebuild part of our system, particularly in the western part of the state. That restoration process will be measured in weeks, not days," said FPL spokesman Rob Gould at a news conference.
Large utilities that serve other parts of the state, including units of Duke Energy Corp, Southern Co and Emera Inc have had scattered outages.
Duke warned its 1.8 million customers in northern and central Florida that outages could exceed 1 million. Emera's Tampa Electric utility said the storm could affect up to 500,000 of the 730,000 homes and businesses it serves.
The utilities had thousands of workers - some from as far away as California - ready to help restore power once Irma's high winds pass their service areas. About 17,000 were helping FPL, nearly 8,000 at Duke and more than 1,300 at Emera.
FPL said on Friday that Irma could affect around 4.1 million customers, but that was before the storm track shifted away from the eastern side of the state. Its customers are concentrated in Miami-Dade, Broward and Palm Beach counties.
Last October, Hurricane Matthew knocked out 1.2 million FPL customers as it skirted Florida's east coast without making landfall. Matthew did not come on shore and damage infrastructure, and it took the utility about two days to restore power.
FPL has warned customers to prepare for outages that could last weeks if Irma requires the utility to rebuild parts of its service territory.
FPL decided to shut only one of the two reactors at its Turkey Point nuclear plant on Saturday because the storm track shifted, and plans to leave both reactors at the St. Lucie plant in service because hurricane force winds are no longer expected to hit the sites. On Sunday, Gould said its nuclear plants were safe.
FPL, a unit of Florida energy company NextEra Energy Inc , had said on Friday it planned to shut both units at Turkey Point sometime on Saturday about 24 hours before hurricane force winds reached the plant.
St. Lucie is located on a barrier island on the state's east coast, about 120 miles (193 km) north of Miami, while Turkey Point is about 30 miles south of Miami.
Duke said there is spent nuclear fuel at its Crystal River plant, located about 90 miles north of Tampa. The plant, which is on Irma's current forecast track, stopped operating in 2009 and retired in 2013. In a worst case scenario, the spent fuel in the pool could release radiation if exposed to the air, but a federal nuclear official said that was extremely unlikely.
"There is nothing to indicate there is any concern for the spent fuel stored at Crystal River. That fuel is so cold, relatively speaking, it would take weeks before there would be any concern," said Scott Burnell at the U.S. Nuclear Regulatory Commission.
Duke was transferring the spent fuel in the pool at Crystal River to dry cask storage as part of the work to decommission the plant, but temporarily suspended the effort ahead of Irma. (Reporting by Scott DiSavino in New York; Editing by Jeffrey Benkoe)