Residents in the normally balmy US state of Florida swapped their bikinis for bobble hats on Thursday, as temperatures plummeted toward record lows.

Swathes of the state -- famous for its oranges, alligators and retirees seeking year-round sun -- faced near freezing temperatures.

As Floridians raced to uncover long-unused jackets, farmers battled to salvage some of the temperate and tropical crop that form the backbone of the local economy.

Citrus growers feared their 9.3-billion-dollar-a-year industry could be hit hard. Local media reported that as many has four harvests could already be ruined.

Tourism, Florida's other major earner, also was hit.

On Thursday the terraces of Miami's Ocean Drive, normally replete with Mojito-downing tourists, were deserted, as patrons opted to sip hot chocolate indoors.

Cruise operators offering Caribbean beach trips that depart from Miami were also caught off-guard by the intemperate cold snap.

"It is a strange situation," Royal Caribbean's Cintia Martinez told AFP, "but many people come from cold climates, so they are adjusting well. Luckily the places where we travel are not so badly affected."