Frenchman Alain Bernard's 100 metres freestyle world record has been called into question by Australia's head coach, who believes the Olympic champion set the time in an illegal suit.

Wearing a prototype suit pending approval from swimming authorities, Bernard became the first man to break the 47-second barrier in the semi-finals of the French championships in Montpellier on Friday.

The Frenchman's 46.94-second dash smashed the previous record set by Australian Eamon Sullivan at the Beijing Games last year.

"I think it would set a dangerous precedent if this was approved and everyone will be watching it," Alan Thompson said yesterday.

"It's a bit like the situation when Libby (Trickett) broke the world record racing Michael Phelps and her record was not ratified.

"That was not an approved event and this is not an approved suit."

After the record-breaking swim, Bernard was soundly beaten by Frederick Bousquet by 0.36 seconds in the final, after eschewing the unapproved suit for an older one.

Bernard said the slower swim, more than half a second shy of his semi-final result, was due to nerves and a problem with his goggles.