A lusty US couple have been jailed after having sex on a beach in front of "appalled" sunbathers.

Elissa Alvarez, 20, and Jose Caballero, 39, were caught in action by a grandmother who filmed their 25-minute romp on Bradenton Beach in Florida and handed it as evidence to police.

"I've lived here since 1978 and I go to the beaches, and I've never seen anything like this," the woman, who did not want to be named, said.

The pair admitted to lewd behaviour and were sentenced for two and half years on July 6, 2015.

Police said a four-year-old girl was one of the witnesses. At first no-one called the police despite being appalled by their actions.

But the woman contacted officers as soon as they started becoming frisky again after taking a dip in the sea.

"They laid on the beach and passed out for hours. We thought they were dead," the woman added. "But when they woke up, they cuddled for a while - then they started into the same thing they did before."

The pair were eventually arrested in the city of Bradenton. They have been told to register as sex offenders.

elissa alvarez
Elissa Alvarez and Jose Caballero