At least 10 people died after Hurricane Milton sent tornadoes spinning as it ripped across Florida, with flooding swamping swathes of the Tampa Bay area, authorities said on Thursday.

The hurricane carved across the state late on Wednesday before roaring into the Atlantic, leaving behind roads blocked by downed trees and powerlines. Some three million homes and businesses were without power.

So far, though, it appeared that tornadoes, rather than floodwaters, have been responsible for the storm's deaths.

"It was pretty scary," said Susan Stepp, a 70-year-old resident of Fort Pierce, a city on Florida's east coast where four people in a senior living community died after a tornado spawned by Milton struck on Wednesday.

"They did find some people just outside dead, in a tree," she said. "I wish they would have evacuated."

The deaths included five in St Lucie County, three in Volusia County and two in the city of St Petersburg, local authorities said. Homeland Security Secretary Alejandro Mayorkas told reporters the deaths "were caused by the tornadoes."

In Polk County, a member of a road crew was struck and killed by a colleague as he removed a downed tree.

Stepp's husband Bill said a tornado "picked up my 22-ton motor home and threw it across the yard."

"Scary and heartbreaking at the same time, to see much damage and all things you really love just gone, but it's only things and we're still here," the 72-year-old said.

The southeastern US state was able to avoid the level of catastrophic devastation officials had feared.

"The storm was significant, but thankfully this was not the worst-case scenario," Florida Governor Ron DeSantis told a news conference.

Milton made landfall on the Florida Gulf Coast as a major Category 3 storm, with powerful winds smashing communities still reeling from Hurricane Helene which hit only two weeks ago, killing 237 people in the United States.

The National Weather Service issued 126 tornado warnings across the state on Wednesday, "the most ever issued for a single calendar day for the state in records dating back to 1986," wrote hurricane expert Michael Lowry.

As of Thursday evening, rescue operations continued as workers evacuated residents stranded by floodwaters in the city of Clearwater, near Tampa.

"We don't know whether we can come back," Justino Torres, 58, said shortly after crews evacuated him from a building.

"I'm going to leave it in the hands of God."

In nearby Sarasota Bay, Kristin Joyce, a 72-year-old interior designer who also did not evacuate, took photos of tree branches snapped by the wind.

"There is no question it needs to be a serious wake-up call for everyone in terms of climate change," she said, surveying the damage.

Scientists say extreme rainfall and destructive storms are occurring with greater severity and frequency as temperatures rise due to climate change. As warmer ocean surfaces release more water vapour, they provide more energy for storms as they form.

President Joe Biden, who said he spoke with DeSantis on Thursday, urged people to stay inside in the aftermath of the storm, with downed power lines and debris "creating dangerous conditions."

In a video posted on social media, Republican presidential candidate Donald Trump said he and his wife Melania were praying for Florida residents affected by the storm and urged them to vote for him.

"Hopefully, on January 20th you're going to have somebody that's really going to help you and help you like never before," the former president said, referring to the presidential inauguration date.

Hurricane Helene struck Florida late last month, and the back-to-back storms have become election fodder as Trump spreads conspiracy theories claiming Biden and Democratic presidential candidate Kamala Harris are abandoning victims.

That prompted a furious response from Biden who on Wednesday called Trump "reckless, irresponsible."

In Cocoa Beach, on Florida's east coast, one tornado swept in from the ocean, blowing out almost all the windows of a hair salon and tearing a chunk of roof off a bank.

Katherine and Larry Hingle said they were on their porch, watching water from a nearby river rise, when the tornado came through on Wednesday evening.

"I said 'it sounds like a train's coming,'" Katherine, 53, said while out to walk their dog and survey the damage.

In Sarasota, resident Carrie Elizabeth expressed the feelings of many – that despite the violent night, Milton was not quite as bad as had been feared.

"I feel that we're very lucky," she said. "It'll take a long time to clean up, but it could have been much worse." (AFP)