By Erin Ailworth
Nearly 65% of utility customers in Florida, or 6.7 million, were without power Monday evening as Irma passed over the northern part of state and into Georgia as a tropical storm, the state's disaster agency said.
As the storm moved to Atlanta Monday, it caused outages for more than a million customers across Georgia.
Customers of Florida Power & Light Co., a unit of NextEra Energy Inc. and the state's largest investor-owned utility, were the most affected by outages. As of Monday morning, nearly 4.5 million of the company's nearly 5 million customers were without power, according to a company outage map.
Eric Silagy, chief executive of FPL, said Irma had caused more than 5 million outages so far -- a number he called unprecedented for the company -- and the company was expecting more power losses as Irma moved farther north. He continued to warn that many could be without power for weeks.
"You need to understand particularly if there's structural damage it absolutely could be weeks if we have to rebuild parts of the system," said Mr. Silagy, who estimated that the FPL outages affected about 9 million people. "It's not over. We still have customers in north Florida that are losing power because of the storm."
At Gulf Power, a Southern Co. unit that serves just over 455,000 in northwest Florida, spokesman Rick DelaHaya said Monday that the brunt of Irma was just starting to arrive in that region.
"It's supposed to get really bad here in the next couple of hours, and after that we'll make a decision of where we need to get on the road," he said. "With any storm like this, there are going to be some outages."
In the parts of Florida where the weather had started to clear, utilities had crews out to assess the damage wrought by the storm, which hit the state as a hurricane. In advance of Irma, the utilities had called on thousands of repair workers from across the U.S. and had been staging them in areas where the storm was expected to do its worst.
Ana Gibbs, a spokeswoman with Duke Energy Corp., the state's second-largest investor-owned utility, said the company had been given the all clear to start work in the Tampa and Orlando areas. Both took harder-than-expected hits from Irma as the storm's track shift west and then east again. She said customers would likely see trucks passing through their neighborhoods to take stock before repair crews are sent in.
"They assess, they call back to dispatch and let them know what materials are needed, and that's when you see the bucket trucks roll in, " Ms. Gibbs said. "The plan for today is getting through the damage assessment."
As of Monday evening, roughly 1.2 million Duke customers were still affected by outages.
Cherie Jacobs, a spokeswoman for Tampa Electric, a unit of Emera Inc., said her company was in much the same mode. The utility had estimated that up to 500,000 of its customers might lose power. As of Monday evening, more than 320,000 were going without, according to a company outage map.
"There's damage assessors looking at exactly what we are dealing with -- they are on land and in the air," Ms. Jacobs said. "We also have restoration crews in the field beginning work."
Georgia Power, a subsidiary of Southern Co., said it expected "widespread, extensive damage due to high winds, heavy rain and fallen trees" and was prepared to mobilize roughly 3,400 repair workers. A company outage map showed just over 748,000 customers without power shortly after 5 p.m. Monday. Georgia Power serves 2.5 million customers.
Meanwhile, an outage map kept by Georgia EMC, a trade association representing the state's 41 electric cooperatives, showed more than 471,000 affected by power outages. Those cooperatives serve 4.4 million people.
Write to Erin Ailworth at Erin.Ailworth@wsj.com