(CNN) As night fell Tuesday, many people from South Carolina to Florida were staying in darkened homes, dealing with fallen trees and blocked roadways, and hoping they could find gas.

The situation in the Sunshine State was trying the patience of people who rode out the storm and those who came home after evacuating Hurricane Irma's path to find widespread devastation and access to their neighborhoods limited at times.

Power outages in Florida affected almost 5 million homes, organizations and businesses, among them gas stations, which need the electricity to keep pumps working.

Two days after Irma made landfall on Cudjoe Key, authorities and a few residents were finally able to reach some of the Florida Keys on Tuesday.

What they found was devastating: Based on initial estimates, 25% of the houses on the chain of islands have been destroyed, the Federal Emergency Management Agency said Tuesday. Another 65% suffered major damage.

"Basically, every house in the Keys was impacted some way," FEMA Administrator Brock Long said.

But Key West City Manager Jim Scholl told CNN that FEMA's estimates might be high. The damage in his city and in his neighborhood on Cudjoe Key didn't match those dire numbers, he said.

The biggest challenge in Key West is moving debris out of the roadways. Scholl said he felt sympathy for the people who want to come home, but aren't being allowed this far south because of issues with the water infrastructure. The area is under a boil water advisory.

"That's why we don't want people to, en masse, return down here to the Keys. And we certainly understand the frustration," he said. "Everyone wants to get down here and check out their homes."

It's a long wait for those sifting through what's left of their homes throughout Florida in the oppressive heat and high humidity -- doing so while they wait for the power, and thus the air conditioning, to come back on.

All customers who lost electricity on the eastern side of the state will likely have power restored by the end of this weekend, because fewer electrical poles came down in the storm, Florida Power & Light said Tuesday.

An FPL official told reporters at a Broward County news conference that of the 790,000 customers in that county who lost power, 330,000 had their electricity restored Tuesday.

The company is focusing its efforts first on schools, hospitals and other critical infrastructure. Gas stations and restaurants are next on the plan, the official said.

Customers on the west coast of Florida, where Hurricane Irma made its final landfall, will likely have power restored by September 22, the company has said.

JUST WATCHED Cuomo: Nothing left untouched in the Keys Replay More Videos ... MUST WATCH Cuomo: Nothing left untouched in the Keys 01:30

But residents like William Rose have bigger concerns. Rose still can't reach his family on the Florida Keys, where about a quarter of the islands' houses are annihilated.

He's not sure whether his mother, stepdad, grandmother and aunt survived Irma's wrath.

"I have no idea, but I'm trying to stay positive," Rose said.

Before the Keys lost cellphone service, Rose received a text from his mother, who chose not to evacuate.

"This is terrible. I will never do this again," the text read. "I'm so glad you got out."

Roadwork in the Keys

The Florida Department of Transportation said Tuesday night it has determined the bridges between the islands are structurally sound.

JUST WATCHED Widespread destruction in the Florida Keys Replay More Videos ... MUST WATCH Widespread destruction in the Florida Keys 01:19

Transportation officials said two sections of US 1 that were washed away by Irma, one at mile marker 37 and the other at mile marker 75, have been repaired.

Darwin Tabacco, who stayed on Big Pine Key during Irma, is one of the fortunate residents. Both he and his house survived.

"A lot of people lost everything," he said Tuesday morning. "There's homes blown off the stilts. There's power lines down all over the place. Trees completely uprooted. People's businesses flooded. Septic fields flooding. It's just terrible."

Millions without power

Photos: Hurricane Irma slams Florida Children clean a dirty mattress from a flooded home in Immokalee, Florida, on Thursday, September 14. Hurricane Irma laid waste to beautiful Caribbean islands and caused historic destruction across Florida. The cleanup will take weeks; recovery will take months. Hide Caption 1 of 58 Photos: Hurricane Irma slams Florida On September 14, President Donald Trump, Vice President Mike Pence and first lady Melania Trump hand out food to people impacted by Hurricane Irma in Naples, Florida. Hide Caption 2 of 58 Photos: Hurricane Irma slams Florida Debris litters the area around a group of homes in the Florida Keys on Wednesday, September 13. Hide Caption 3 of 58 Photos: Hurricane Irma slams Florida Lake County jail inmates fill sandbags in Astor, Florida, on September 13. Hide Caption 4 of 58 Photos: Hurricane Irma slams Florida A classic Volkswagen sits in floodwaters September 13 in Middleburg, Florida. Flooding from the Black Creek topped the previous high-water mark by about 7 feet. Hide Caption 5 of 58 Photos: Hurricane Irma slams Florida James Wade checks for water-damaged items as floodwaters recede in Middleburg on September 13. Hide Caption 6 of 58 Photos: Hurricane Irma slams Florida Floodwaters surround vehicles in Callahan, Florida, on Tuesday, September 12. Hide Caption 7 of 58 Photos: Hurricane Irma slams Florida Jose Encarnacion pulls a chicken from a cage as he gathers belongings from his flooded house in Bonita Springs, Florida, on September 12. Hide Caption 8 of 58 Photos: Hurricane Irma slams Florida Joseph Dupuis III stacks boxes off the floor in his parents' water-logged apartment in Jacksonville, Florida, on September 12. Hide Caption 9 of 58 Photos: Hurricane Irma slams Florida Motorists in Estero, Florida, fill gas cans September 12, moments before police shut the station down because of a curfew. Hide Caption 10 of 58 Photos: Hurricane Irma slams Florida Mike Gilbert and his daughter Brooke embrace in front of a relative's destroyed condominium building in the Florida Keys on September 12. Hide Caption 11 of 58 Photos: Hurricane Irma slams Florida Members of the US Coast Guard operate in floodwaters during rescue missions in Hastings, Florida, on September 12. Hide Caption 12 of 58 Photos: Hurricane Irma slams Florida Waist-deep in floodwater, Shelly Hughes gets her first look at the inside of her camper in Arcadia, Florida, on September 12. Hide Caption 13 of 58 Photos: Hurricane Irma slams Florida In the aftermath of Hurricane Irma, a house slides into the Atlantic Ocean in Ponte Vedra Beach, Florida, on Monday, September 11. Hide Caption 14 of 58 Photos: Hurricane Irma slams Florida Richard Shieldhouse maneuvers through storm-surge floodwaters in Jacksonville on September 11. Hide Caption 15 of 58 Photos: Hurricane Irma slams Florida Mario Valentine sits in his badly damaged home in Immokalee on September 11. Hide Caption 16 of 58 Photos: Hurricane Irma slams Florida Boats are partially submerged in Key Largo, Florida, on September 11. Hide Caption 17 of 58 Photos: Hurricane Irma slams Florida Chris Stokes works in the mud as he helps clean up damage to his father's convenience store in Everglades City, Florida, on September 11. Hide Caption 18 of 58 Photos: Hurricane Irma slams Florida Ashley Tomberg drags a tree branch from the roof of a neighbor's house in Gainesville, Florida, on September 11. Hide Caption 19 of 58 Photos: Hurricane Irma slams Florida Floodwaters inundate a car in Jacksonville on September 11. Hide Caption 20 of 58 Photos: Hurricane Irma slams Florida A crocodile appears at the Dinner Key Marina in Miami on September 11. Hide Caption 21 of 58 Photos: Hurricane Irma slams Florida John Duke tries to salvage his flooded vehicle in Jacksonville on September 11. Hide Caption 22 of 58 Photos: Hurricane Irma slams Florida A van sits in a sinkhole that opened up in Winter Springs, Florida, on September 11. Hide Caption 23 of 58 Photos: Hurricane Irma slams Florida People check out floodwaters at Jacksonville's Memorial Park on September 11. Hide Caption 24 of 58 Photos: Hurricane Irma slams Florida Kelly McClenthen and her boyfriend, Daniel Harrison, walk through floodwaters in Bonita Springs on September 11. Hide Caption 25 of 58 Photos: Hurricane Irma slams Florida A truck drives through a flooded street in Key Largo on September 11. Hide Caption 26 of 58 Photos: Hurricane Irma slams Florida A man walks by damage in Palm Shores, Florida, on September 11. Hide Caption 27 of 58 Photos: Hurricane Irma slams Florida Catharine Taylor Woods cleans up a broken awning outside her building in Wauchula, Florida, on September 11. Hide Caption 28 of 58 Photos: Hurricane Irma slams Florida The roof of a home is damaged in Marco Island, Florida, on September 11. Hide Caption 29 of 58 Photos: Hurricane Irma slams Florida Rick Freedman checks damage to his neighbor's home in Marco Island on September 11. Hide Caption 30 of 58 Photos: Hurricane Irma slams Florida Boats are partially submerged in a marina in downtown Miami on September 11. Hide Caption 31 of 58 Photos: Hurricane Irma slams Florida People step out of their flooded home in Fort Myers, Florida, on September 11. Hide Caption 32 of 58 Photos: Hurricane Irma slams Florida A felled tree blocks a street in downtown Miami on September 11. Hide Caption 33 of 58 Photos: Hurricane Irma slams Florida Irma damaged this gas station roof in Bonita Springs. Hide Caption 34 of 58 Photos: Hurricane Irma slams Florida Michele Snelling sleeps on couch cushions next to her 4-month-old daughter, Lauryn, at a middle school in St. Petersburg, Florida, on September 11. The school was filled with evacuees. Hide Caption 35 of 58 Photos: Hurricane Irma slams Florida Hotel guests navigate a dark stairwell after they lost power in Fort Lauderdale, Florida. Hide Caption 36 of 58 Photos: Hurricane Irma slams Florida People in Cape Coral, Florida, tend to a car that flipped over during Hurricane Irma on Sunday, September 10. Hide Caption 37 of 58 Photos: Hurricane Irma slams Florida A manatee lies stranded September 10 after waters receded during Irma's approach in Manatee County, Florida. Hide Caption 38 of 58 Photos: Hurricane Irma slams Florida High winds split this large tree in half in Fort Lauderdale. Hide Caption 39 of 58 Photos: Hurricane Irma slams Florida An American flag is torn as Irma passes through Naples on September 10. Hide Caption 40 of 58 Photos: Hurricane Irma slams Florida A sheriff's deputy walks through a shelter in Naples after the power went out on September 10. Hide Caption 41 of 58 Photos: Hurricane Irma slams Florida A police officer walks over debris after a tornado touched down in Palm Bay, Florida, on September 10. Hide Caption 42 of 58 Photos: Hurricane Irma slams Florida Yaya Lopez holds her fiance, Howard Lopez, while they sleep in a middle-school hallway in St. Petersburg on September 10. Hide Caption 43 of 58 Photos: Hurricane Irma slams Florida Geoff Rutland, a local volunteer from Crossing Jordan Church, helps other residents get ice from a vending machine in Tampa, Florida, on September 10. Hide Caption 44 of 58 Photos: Hurricane Irma slams Florida PJ Pike checks on his boat and one belonging to a friend in Fort Myers. Both were sitting in mud at their moorings due to an unusually low tide on September 10. Hide Caption 45 of 58 Photos: Hurricane Irma slams Florida People walk past a building in Miami where the roof was blown off by Hurricane Irma on September 10. Hide Caption 46 of 58 Photos: Hurricane Irma slams Florida An abandoned car sits in floodwaters during a storm surge in Fort Lauderdale on September 10. Hide Caption 47 of 58 Photos: Hurricane Irma slams Florida Fallen trees block a parking lot in Fort Lauderdale on September 10. Hide Caption 48 of 58 Photos: Hurricane Irma slams Florida Sailboats moored near Watson Island ride out the winds and waves on September 10. Hide Caption 49 of 58 Photos: Hurricane Irma slams Florida Members of the Blinckman family use their personal devices in a stairwell utility closet as Hurricane Irma went over Key West, Florida, on September 10. Hide Caption 50 of 58 Photos: Hurricane Irma slams Florida Evacuees watch the weather from a shelter in Naples on September 10. Hide Caption 51 of 58 Photos: Hurricane Irma slams Florida Heavy winds and rain blow through Miami on September 10. Hide Caption 52 of 58 Photos: Hurricane Irma slams Florida Weather Channel meteorologist Mike Seidel fights fierce winds and flooded streets while reporting in Miami on September 10. Hide Caption 53 of 58 Photos: Hurricane Irma slams Florida A man records the gusty winds going through downtown Miami on September 10. Hide Caption 54 of 58 Photos: Hurricane Irma slams Florida A tree lies on a pickup truck after being knocked down by the high winds in Miami on September 10. Hide Caption 55 of 58 Photos: Hurricane Irma slams Florida Hotel guests eat breakfast by lamplight after the Courtyard Marriott was left without power in Fort Lauderdale on September 10. Hide Caption 56 of 58 Photos: Hurricane Irma slams Florida Part of this crane tower collapsed in Miami on September 10. Hide Caption 57 of 58 Photos: Hurricane Irma slams Florida People sit in the Miami-Dade County Fair Expo Center as Irma approached Miami on Saturday, September 9. See Hurricane Irma's impact on the Caribbean Hide Caption 58 of 58

Massive power outages are crippling much of the Southeast on Tuesday. Among the hardest hit by Irma (as of 9 p.m. ET):

Florida: About 4.4 million customers -- which includes homes, organizations and businesses -- are without power across the state, authorities said.

About 4.4 million customers -- which includes homes, organizations and businesses -- are without power across the state, authorities said. Georgia: Almost 700,000 customers are in the dark, according to Georgia Power and Georgia EMC.

Almost 700,000 customers are in the dark, according to Georgia Power and Georgia EMC. South Carolina: Almost 55,000 customers have no power, according to Duke Energy and SCE&G.

Almost 55,000 customers have no power, according to Duke Energy and SCE&G. North Carolina: More than 29,000 customers don't have electricity, according to Duke Energy.

More than 29,000 customers don't have electricity, according to Duke Energy. Alabama: More than 7,000 customers are without electricity, Alabama Power said.

9 states impacted

Irma, which stretched 650 miles from east to west, has pummeled at least nine states -- deluging city streets, knocking over trees and destroying homes along the way.

At least 16 storm-related deaths have already been reported on the US mainland, according to local officials:

Florida has reported 12 deaths, Alberto C. Moscoso, a spokesman for Florida Division of Emergency Management, said Tuesday evening.

has reported 12 deaths, Alberto C. Moscoso, a spokesman for Florida Division of Emergency Management, said Tuesday evening. Georgia had three deaths. A 62-year-old man who was on his roof was killed in Worth County, which experienced wind gusts of 69 mph. Another man was killed in Sandy Springs when a tree fell on his house. And a woman was killed when a tree struck her vehicle in Cumming.

had three deaths. A 62-year-old man who was on his roof was killed in Worth County, which experienced wind gusts of 69 mph. Another man was killed in Sandy Springs when a tree fell on his house. And a woman was killed when a tree struck her vehicle in Cumming. South Carolina had two deaths. A 57-year-old man was struck by a falling tree limb during the storm. State emergency officials said a driver with a Florida license plate also died from the storm, but did not give further details.

Flights, hospitals will be back online

While the Keys have an exhaustive recovery ahead, signs of normalcy will pop up Tuesday elsewhere in Florida.

And Florida Hospital, a health provider in the state, said it would reopen many of its impacted facilities on Tuesday or Wednesday.

Mammoth flooding

Even a weakened Irma engulfed cities as far north as Charleston, South Carolina, on Tuesday.

JUST WATCHED Irma swamps Jacksonville and Charleston Replay More Videos ... MUST WATCH Irma swamps Jacksonville and Charleston 00:34

"I really didn't expect it to become this bad here," Charleston resident Mike Stusnick said Tuesday. "It came in really fast last night. ... We were just praying that it didn't come all the way into the house, and it didn't."

Jacksonville, Florida -- the largest city by area in the contiguous United States -- is still trying to recover from record-breaking storm surge and flooding on Monday.

More than 300 people have been rescued in Jacksonville, the governor said Tuesday.

"So many areas that you thought wouldn't flood, flooded," Scott said.

Irma's deadly trail -- and questions about climate change

Before slamming into the United States, Irma hit Cuba late Friday as a Category 5 hurricane . Irma killed 38 people in the Caribbean before heading to the United States.

This is the first year on record that the continental United States has had two Category 4 hurricane landfalls in the same year. Last month, Hurricane Harvey devastated much of coastal Texas and killed more than 70 people

At a news conference Tuesday, both the FEMA administrator and acting DHS Secretary Elaine Duke avoided explicitly answering questions about whether Washington needs to focus more on climate change after Harvey and Irma

Instead, Long and Duke stressed the need for preparedness and resiliency.

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