In Cuba, 10 people died when the island was being battered by then-Hurricane Irma, according to state news media.
Most of them died in Havana, which witnessed chest-deep seawater in some neighborhoods.
Several of the deaths occurred in partial building collapses, state media said. Much of Cuba’s housing stock is deteriorating.
At least 24 people died in other parts of the Caribbean as the hurricane blew through. In the US, the storm’s outer bands were also blowing into Georgia, where the storm’s centre was expected to arrive later in the day.
With rough conditions persisting across Florida, many communities in Irma’s wake feared what destruction would be revealed when daylight came.
Winds knocked a utility pole and power lines on to a sheriff’s vehicle in Polk County, east of Tampa, illustrating the dangerous conditions for emergency personnel.
A deputy and a paramedic, who had just escorted an elderly patient to safety, were trapped for two hours until a crew could free them. Both were unhurt.
More than 120 homes were being evacuated in Orange County, just outside the city of Orlando, as floodwaters started to pour in.
Firefighters and the National Guard were going door-to-door and using boats to ferry families to safety.
A few miles away, 30 others had to be evacuated when a 60ft sinkhole opened up under an apartment building. No injuries were reported in either case.
Nearly 4.5 million homes and businesses across Florida lost power and utility officials said it will take weeks to restore electricity to everyone. More than 100,000 were in the dark in Georgia.
Irma’s centre was about 105 miles north of Tampa when forecasters announced it had weakened to a tropical storm. However, they warned its maximum sustained winds were 70mph and the storm was still producing higher gusts.
The monster storm, which arrived in Florida as a Category 4 hurricane, has toppled at least three constructions cranes – two over central Miami and one in Fort Lauderdale.
People in the heavily populated Tampa-St Petersburg area had feared a first direct hit from a major hurricane since 1921, but the storm weakened to a Category 2 as it approached that area.
Tampa mayor Bob Buckhorn said the situation was not as bad as it could have been but warned residents that dangerous storm surge continued.
He also described downed power lines and other debris.
“What we feared the most was the surge,” he said. “The surge is yet to be finished.”
Meanwhile, rescue efforts ramped up in the evacuated neighbourhood near Orlando as Guardsmen in helmets and fatigues rolled through standing water in a high-clearance vehicle.
Firefighters rescued a puppy from one of the homes there and leashed the anxious dog to the front of one of their trucks to give it water and food.
As the sun rose in Orlando, many tried to survey the damage, but authorities warned that conditions remain dangerous and asked people not to venture outside because of a curfew.
No deaths in Florida were immediately linked to the storm.
In the Caribbean, at least 24 people were killed during Irma’s destructive trek across exclusive islands known as the holiday playground for the rich.
In Cuba, the storm swamped Havana’s famous seawall, pushing water nearly a third of a mile inland.
In one of the largest US evacuations, nearly seven million people in the south east were warned to seek shelter, including 6.4 million in Florida alone.
More than 200,000 people waited in shelters across Florida.
At Germain Arena, where thousands sought refuge south of Fort Myers, people sat amid puddles on the concrete floor. Officials said the arena remained in one piece, but wind-driven water leaked in at the height of the storm.
“Irma went over and we were all like, ‘Oh good, we survived.’ And then all of a sudden some of the panels came off the roof, I guess, and we started getting water pouring down in different places,” said 61-year-old Mary Fitzgerald.
“It was was like, ‘Oh my God, what is going to happen?'”
Bryan Koon, Florida’s emergency management director, said late on Sunday that authorities had only scattered information about the storm’s toll.
“I’ve not heard of catastrophic damage. It doesn’t mean it doesn’t exist. It means it hasn’t gotten to us yet,” Mr Koon said.
In the low-lying Keys, where a storm surge of over 10ft was recorded, appliances and furniture were seen floating away, and Monroe County spokeswoman Cammy Clark said the ocean waters were filled with navigation hazards, including sunken boats.
County administrator Roman Gastesi said crews would begin house-to-house searches to check on survivors.
Storm surge and tornadoes were two big concerns.
A tide gauge in Naples reported a 7ft rise in water levels in just 90 minutes late on Sunday.
An apparent tornado spun off by Irma destroyed six mobile homes in Palm Bay, midway up the Atlantic coast. Flooding was reported along Interstate 4, which cuts across Florida’s midsection.
Curfews were imposed overnight in Miami, Tampa, Fort Lauderdale and much of the rest of south Florida, and some arrests of violators were reported.
Miami Beach barred outsiders from the island.
About 30,000 people heeded orders to leave the Keys as the storm closed in but an untold number refused.
John Huston, who stayed in his Key Largo home, watched his garden flood even before the arrival of high tide.
“Small boats floating down the street next to furniture and refrigerators. Very noisy,” he said by text message. “Shingles are coming off.”
Irma is expected to push into Georgia, Alabama, Mississippi, Tennessee and beyond. A tropical storm warning was issued for the first time ever in Atlanta, where many schools cancelled classes.
Irma was once the most powerful hurricane ever recorded in the open Atlantic, a Category 5 with a peak wind speed of 185mph.
For days, forecasters had warned Irma was taking dead aim at Florida.
Irma made landfall as a Category 4 hurricane on Sunday morning at Cudjoe Key, not far from Key West. It then rounded Florida’s south-western corner and hugged the coast closely as it pushed north.