Tropical storm Ian has strengthened into a Category 1 hurricane as it nears north-west Cuba, the US National Hurricane Center said on Monday.
Hurricane Ian has sustained with maximum sustained winds of 120 km/h (75 mph), meteorologists said, warning that "additional rapid strengthening is expected today."
Cuba is expected to bear the initial brunt of the storm, with authorities suspending classes on Monday and evacuating residents Pinar del Rio province.
A hurricane warning has also been issued in the Cuban provinces of Isla de Juventud and Artemisa, as well as in the nearby Cayman Islands.
Florida braces for wild weather
Meteorologists said Ian could potentially make landfall on the west coast of Florida by midweek.
On Sunday, Florida Governor Ron DeSantis declared a state of emergency in all 67 counties and urged residents to stock up on food, water, fuel and medicine. He also mobilized 2,500 National Guard members to help with the emergency response.
"Expect heavy rains, strong winds, flash flooding, storm surge and even isolated tornadoes," DeSantis told reporters.
Hurricane Ian comes just a week after Hurricane Fiona tore through the Caribbean and the coast of Canada, causing widespread destruction.