A US student spent almost three days trapped inside a cave after he was left behind on a university field trip.

Lukas Cavar, 19, was visiting the Sullivan Cave in southern Indiana with the Indiana University Caving Club on Sunday.

He was separated from the rest of the group who then left without him, locking the gated entrance.

"I was very confused and pretty scared," he told the Indiana Daily Student.

"It took me a little while to wrangle my emotions and sort of approach things analytically, sensibly, to come up with a game plan to survive", he said.

He told the student newspaper that he licked moisture off cave walls to stay hydrated and wrote goodbye messages to his family on his mobile phone.

Rigorous protocols

Despite shouting for help, he was not rescued until late on Tuesday night when the president of the Caving Club realised he was missing and returned to the cave.

In a post on Facebook, Mr Cavar said: "Just wanted to let everyone know that I'm safe and sound! Just got rescued about 30 minutes ago. Boy, it's good to be back on the surface!".

The Caving Club said there had been a "failure of leadership".

They said: "We have a series of rigorous protocols in place that are supposed to prevent situations like this, but they are only effective if followed. We had a failure in our leadership to closely follow all these safety procedures."