The US National Weather Service has issued an unlikely warning as temperatures plummet to unusual lows in Florida – beware falling iguanas.

With temperatures predicted to drop to below freezing inland (and only slightly warmer in coastal Florida), the service said iguanas could fall from trees as they slowed down in the cold.

“This isn’t something we usually forecast, but don’t be surprised if you see iguanas falling from the trees tonight as lows drop into the 30s and 40s [Fahrenheit],” the weather service tweeted on Tuesday (local time).

“They may fall from trees, but they are not dead.”

Jan 21 – This isn't something we usually forecast, but don't be surprised if you see Iguanas falling from the trees tonight as lows drop into the 30s and 40s. Brrrr! #flwx #miami pic.twitter.com/rsbzNMgO01

— NWS Miami (@NWSMiami) January 21, 2020

Chris Michaels, a meteorologist with WSLS-TV in Norfolk, Virginia, told USA Today that iguanas stiffened up once temperatures dropped to certain lows.

The phenomenon had been observed previously in south Florida, he said.

“At about [10 degrees Celsius], iguanas can become lethargic,” Mr Michaels said.

“It’s when the temperature drops to about [4 degrees] or lower that their blood doesn’t move around as quickly. As a result, they can stiffen up and fall out of the trees they frequent.”

During a similar cold snap in January 2018, well-meaning residents who found stiffened iguanas were advised to leave them alone, as they can feel threatened and bite once they warm up.

“Don’t assume that they’re dead,” said Kristen Sommers, who oversees the Florida Fish and Wildlife Conservation Commission’s non-native fish and wildlife program.

Green iguanas are considered an invasive species in Florida.

They eat through gardens and dig burrows that undermine infrastructure.