Hours after Idalia slammed ashore as a powerful Category 3 hurricane at Keaton Beach in Florida’s Big Bend region packing winds of about 201kph, authorities were still trying to assess the full extent of damage in the hardest-hit areas.

Video footage and photographs from the region around Idalia’s landfall showed ocean waters washing over highways and neighbourhoods swamped by extensive flooding at midday.

At an afternoon news conference, Florida Governor Ron DeSantis said there were no immediate reports of hurricane fatalities and it seemed most residents in vulnerable, low-lying areas had heeded evacuation orders and warnings to move to higher ground.

DeSantis was speaking in Perry, a town that lies about 35km north of where Idalia came ashore and bore some of the storm’s worst damage. Electricity was out across the community, businesses were all shuttered and many homes were empty.

Here and there, residents were seen clearing fallen trees and limbs that littered yards and streets, making it difficult to drive through the town. Some homes and other buildings were left in shambles.

Thomas Demps (80), a Taylor County commissioner, let out a long, stunned whistle and several exclamations of “Oh, my!” as he walked around his Mount Olive Missionary Baptist Church in Perry on Wednesday afternoon.

The church took a beating, Perry said, with missing shingles, portions of outside walls torn away and water standing on the inside floor.

“This is the worst storm I’ve ever seen here, never seen it this bad,” said Demps, a retired industrial mechanic.

At least 75 people were rescued from floodwaters in St Petersburg, city officials said on social media, with video posted showing two emergency workers in a small boat traveling through a flooded neighbourhood in heavy rains.

In Valdosta, Georgia, about 128km northeast of Tallahassee, Florida’s state capital, emergency boat crews were carrying out rescues of residents trapped in homes, according to the city’s Facebook page. No other details were immediately available.

Feeding on the warm, open waters of the Gulf Mexico as it churned towards Florida, gaining strength after skirting western Cuba on Monday as a tropical storm, Idalia unleashed destructive winds and torrential downpours that were forecast to cause flooding up to 5m deep along Florida’s Gulf Coast.

By early Wednesday afternoon, the eye of Idalia had left Florida, though parts of the state, particularly in the north, were still being buffetted by storm bands, DeSantis said.

Florida’s Gulf Coast, southeastern Georgia and eastern parts of North and South Carolina were forecast to receive 10cm-20cm of rain through Thursday, with isolated areas seeing as much as a foot of rain, the National Hurricane Center (NHC) warned.

Georgia authorities were monitoring the system as it entered the state.

“Hopefully, it’s out of the state by 8pm this evening, maybe 10 o’clock, and then that we can begin to assess for those that were hit first,” state Emergency Management Agency Director James C Stallings said at a briefing on Wednesday.

Cedric King, a businessman from coastal Brunswick, Georgia, just south of Savannah, was not going to take chances.

“I packed up the family and headed north,” he said after a five-hour drive with his mother, wife and children. “We evacuated.”

The storm’s most dangerous feature is a powerful surge of wind-driven surf that is expected to flood low-lying areas, officials said.

By mid-morning, a National Oceanic and Atmospheric Administration monitoring station in Steinhatchee, 32km south of Keaton Beach, showed waters reaching 2.4m, well above the 1.8m flood stage. Stations in the more densely populated Tampa area showed “minor flooding” at 10am.

In Hillsborough County, an area of 1.5 million people south of the Big Bend region that includes Tampa, crews were dealing with widespread damage and flooded streets, officials said in a news briefing.

“Folks, this storm is not over. If you are in a safe location, please remain there,” said Emergency Management Director Timothy Dudley, noting that local waterways would crest at high tide at 2.30pm.

Overnight, Idalia attained “an extremely dangerous Category 4 intensity” on the five-step Saffir-Simpson wind scale, but by 7am the storm weakened slightly into Category 3 with maximum sustained winds of 201kph, the NHC said.

As it entered southeastern Georgia, Idalia’s wind speeds ebbed to 144kph, reducing the tempest to a Category 1 storm. By 5pm EDT, it weakened further into a tropical storm, the NHC said.

TWO DEATHS REPORTED IN FLORIDA

Two motorists died in separate rain-related crashes on Wednesday morning, according to the Florida Highway Patrol. In Wednesday afternoon’s press briefing, DeSantis said he only knew of “unconfirmed” reports of storm-caused fatalities.

Florida Transportation Secretary Jared Perdue said at the briefing that the state’s National Guard was conducting water rescues from vehicles in Hernando and Taylor counties.

About 1,000 bridges are expected to be inspected in northern Florida on Wednesday before they can reopen, Perdue added.

More than 280,000 homes and businesses were without power in Florida as of midday and 160,000 customers were similarly affected in Georgia, Poweroutage.us reported.

(Reporting by Marco Bello and Maria Alejandra Cardona.)