Parts of Florida are inching back towards normality with workers restoring power, clearing roads and replenishing fuel supplies, even as teams scour the southernmost islands and authorities warn of mass devastation.

Residents drifted back from shelters and far-away havens to see Hurricane Irma’s scattershot destruction.

Flooded streets remained, and the count of damaged and destroyed homes rose even as some curfews were lifted, flights resumed and amusement park rides rode again.

As crews laboured to repair the lone highway connecting the Keys, residents of some of the islands closest to Florida’s mainland were allowed to return and get their first look at the devastation two days after Irma roared in with 130mph winds.

Federal Emergency Management Agency administrator Brock Long said preliminary estimates suggested that 25% of homes in the Keys were destroyed and 65% sustained major damage.

“Basically, every house in the Keys was impacted,” he said.

The number of deaths blamed on Irma in Florida climbed to 12, in addition to four in South Carolina and two in Georgia. At least 37 people were killed in the Caribbean.

“We’ve got a lot of work to do, but everybody’s going to come together,” Florida governor Rick Scott said. “We’re going to get this state rebuilt.”

Glimpses of Irma’s economic toll were emerging, with Florida saying 31 state agencies had already amassed nearly 250 million dollars (£190 million) in preparation and recovery expenses.

The number of people without electricity in the steamy late-summer heat dropped to 9.5 million — just under half of Florida’s population. Utility officials warned it could take 10 days or more for power to be fully restored.

About 110,000 people remain in shelters across the state.

While nearly all of Florida was engulfed by the 400 mile-wide storm, the Keys — home to about 70,000 people — appeared to be hardest hit. Drinking water and power were cut off, all three of the islands’ hospitals were closed, and the supply of fuel was extremely limited.

Search-and-rescue teams made their way into the more distant reaches of the Keys, and an aircraft carrier was positioned off Key West to help. Officials said it was not known how many people ignored evacuation orders and stayed behind in the Keys.

Crews also worked to repair two washed-out, 300ft sections of US 1, the highway that runs through the Keys, and check the safety of the 42 bridges linking the islands.

The Lower Keys — including the chain’s most distant and most populous island, Key West, with 27,000 people — were still off-limits, with a roadblock in place where the highway was washed out.