DNA tests have confirmed that three man-eating Nile crocodiles have been found living in Florida's swamps.

Unlike local alligators, the species preys on humans and is thought to be responsible for up to 200 deaths a year at home in sub-Saharan Africa.

It is possible more of the beasts are at large in the state, experts say.

It is not known for certain how they reached the US. "They didn't swim from Africa," said University of Florida herpetologist Kenneth Krysko.

One likely possibility was that they were brought in illegally by unlicensed collectors, who then failed to keep them secured or intentionally released them, Mr Krysko told the Associated Press news agency.