Read the latest on the storm with Tuesday’s live updates on Irma.

Florida emerged from Hurricane Irma on Monday as a landscape of blacked-out cities, shuttered gas stations, shattered trees and flooded streets, while the now-weakened storm kept sweeping northward.

Major streets remained underwater in cities from Miami to Jacksonville, with even more roads snarled by debris. As many as nine million Floridians lost electricity at some point during the storm, and the chief executive of a major utility, Florida Power & Light, said that it could take weeks to restore full service.

Officials were still assessing Irma’s impact in the Florida Keys, which may have borne the worst of the storm. After a survey of the islands, Gov. Rick Scott told reporters that he had seen crippling damage there, including countless overturned trailers and many boats washed ashore. Recovery in the Keys would be a “long road,” he said.

“I just hope everybody survived,” Mr. Scott said. “It’s horrible, what we saw.”

Later on Monday, the Defense Department said that damage to the Keys was so extensive that it might be necessary to evacuate the 10,000 residents who rode out the storm on the islands.