American surfer Kelly Slater has admitted that he feels "nervous" before every heat as he bids to clinch the world title.

The 42-year-old came back from a blip in the first round of the championship tour event in France by beating fellow American Dane Reynolds in round two.

"I'm nervous about each heat now," ABC News quotes Slater as saying. "I've been coming to France to surf for 25 years now and I'm about as comfortable as one can get.

"The tide, waves, wind, banks and general conditions are always changing so you're never overly confident."

Slater has been crowned world champion 11 times in his career.