Hurricane Idalia made landfall on Florida's west coast as a dangerous Category 3 storm on Wednesday and was unleashing life-threatening storm surges and rainfall in an area not accustomed to such pummelling.

Idalia came ashore in the lightly populated Big Bend region, where the Florida Panhandle curves into the peninsula.

Two people were killed in weather-related car crashes in Florida on Wednesday morning, the Florida Highway Patrol said.

In one incident in Pasco County, a 40-year-old male driver died after losing control of a Ford Ranger and colliding with a tree, the highway patrol said in a statement.

In Alachua County, a 59-year-old male driving a Toyota Tacoma crashed into trees in "extremely rainy conditions" and was killed, the highway patrol said.

Florida residents living in vulnerable coastal areas were ordered to pack up and leave as Idalia gained strength in the warm waters of the Gulf of Mexico.

And those who didn't were warned to find a safe place while the storm moved through.

“Don't put your life at risk by doing anything dumb at this point,” Gov. Ron DeSantis said at a news conference Wednesday morning. “This thing's powerful. If you're inside, just hunker down until it gets past you.”

Storm surge could rise as high as 4.5 metres in some places.

The 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.