Authorities urge residents to prepare for Ian that is forecast to become a major hurricane within days as it tracks toward the US state.

Ian is forecast to become a hurricane on Sunday and a major hurricane by late Monday or early Tuesday.
Ian is forecast to become a hurricane on Sunday and a major hurricane by late Monday or early Tuesday. (AP)

Governor Ron DeSantis has declared a state of emergency for all of Florida as Tropical Storm Ian gains strength over the Caribbean and is forecast to become a major hurricane within days as it tracks toward the state.

DeSantis had initially issued the emergency order for two dozen counties on Friday. But he expanded the warning on Saturday to the entire state, urging residents to prepare for a storm that could lash large swaths of Florida.

"This storm has the potential to strengthen into a major hurricane and we encourage all Floridians to make their preparations," DeSantis said in a statement.

"We are coordinating with all state and local government partners to track potential impacts of this storm."

The National Hurricane Center said Ian is forecast to rapidly strengthen in the coming days before moving over western Cuba and toward the west coast of Florida and the Florida Panhandle by the middle of next week.

It added that Ian was forecast to become a hurricane on Sunday and a major hurricane by late Monday or early Tuesday. Ian on Saturday evening had top sustained winds of 75 kph as it swirled about 370 kilometres south of Kingston, Jamaica.

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Storm surge, floods, strong winds risk

John Cangialosi, a senior hurricane specialist at the Miami-based hurricane center, said it wasn't yet clear exactly where Ian will hit hardest in Florida. He said the state's residents should begin preparing for the storm, including gathering supplies for potential power outages.

"Too soon to say if it's going to be a southeast Florida problem or a central Florida problem or just the entire state," he said. 

"So at this point really the right message for those living in Florida is that you have to watch forecasts and get ready and prepare yourself for potential impact from this tropical system."

The governor's declaration frees up emergency protective funding and activates members of the Florida National Guard, his office said.

His order stresses that there is risk for a storm surge, flooding, dangerous winds and other weather conditions throughout the state.

READ MORE: Fiona rampage cuts water access to half a million in Puerto Rico

Source: AP