Hurricane Idalia has strengthened to a dangerous Category 4 storm as it heads toward Florida’s Big Bend region, threatening to unleash life-threatening storm surges and rainfall.

Idalia was projected to come ashore early on Wednesday as a Category 4 storm with sustained winds of at least 130mph in the lightly populated Big Bend region, where the Florida Panhandle curves into the peninsula.

The result could be a big blow to the US state still dealing with lingering damage from last year’s Hurricane Ian.

The US National Weather Service in Tallahassee called Idalia “an unprecedented event” since no major hurricanes on record have ever passed through the bay abutting the Big Bend.

Hurricanes are measured on a five category scale, with a Category 5 being the strongest. A Category 3 storm is the first on the scale considered a major hurricane.

The National Hurricane Centre said “catastrophic damage will occur” during a Category 4 storm.

On the island of Cedar Key, commissioner Sue Colson joined other city officials in packing up documents and electronics at City Hall on Tuesday.

Ms Colson had a message for the almost 900 residents who were under mandatory orders to evacuate. More than a dozen state troopers went door to door warning residents that storm surge could rise as high as 15ft.

She said: “One word: Leave. It’s not something to discuss.”

Governor Ron DeSantis repeated the warning at a Tuesday afternoon news conference.

“You really gotta go now. Now is the time,” he said.

Earlier, the governor stressed that residents did not necessarily need to leave the state, but should “get to higher ground in a safe structure”.

Tolls have been waived on major roads out of the danger area, shelters were open and hotels prepared to take in evacuees.

More than 30,000 utility workers were gathering to make repairs as quickly as possible in the hurricane’s wake. About 5,500 US National Guard troops have also been activated.

After landing in the Big Bend region, Idalia is forecast to cross the Florida peninsula and then drench southern Georgia and the Carolinas on Thursday.

Both Georgia governor Brian Kemp and his South Carolina counterpart Henry McMaster announced states of emergency, freeing up state resources and personnel, including hundreds of National Guard troops.

Idalia pummelled Cuba with heavy rains on Monday and Tuesday, leaving the tobacco-growing province of Pinar del Rio underwater and many of its residents without power.

State media did not report any deaths or major damage.

With a large stretch of Florida’s western coast at risk for storm surges and floods, evacuation notices were issued in 22 counties, with mandatory orders for some people in eight of those counties.

US President Joe Biden said he had spoken to Mr DeSantis and “provided him with everything that he possibly needs”.

Hurricane Ian was responsible for almost 150 deaths last year. The Category 5 hurricane damaged 52,000 structures, nearly 20,000 of which were destroyed or severely damaged.

The National Oceanic and Atmospheric Administration recently said the 2023 hurricane season would be far busier than initially forecast, partly because of extremely warm ocean temperatures.

The season runs through until November 30, with August and September typically the peak.