Milton has rapidly strengthened into a Category 4 hurricane as it heads towards population centres in the US state of Florida, including Tampa and Orlando.

The hurricane threatens a dangerous storm surge in Tampa Bay and sets the stage for potential mass evacuations less than two weeks after the catastrophic Hurricane Helene swamped the coastline.

Milton had maximum sustained winds of 150mph over the southern Gulf of Mexico, the US National Hurricane Centre in Miami said.

Evacuations are being prepared in Florida (NOAA via AP)

The storm could make landfall on Wednesday in the Tampa Bay area and may remain a hurricane as it moves across central Florida towards the Atlantic Ocean.

That path would largely spare other south-eastern US states ravaged by Helene, which caused widespread damage from northern Florida to the Appalachian Mountains and killed at least 230 people.