A performer with the world-famous Cirque du Soleil circus died after plunging from a high wire before a horrified crowd at a Las Vegas show, the organization confirmed on Sunday.

Sarah Guyard, who media reports identified as a 31-year-old mother-of-two, fell to her death towards the end of the circus's popular Ka production staged at the MGM Grand on Saturday.

Witnesses quoted by US media reports said Guyard fell from a height of around 50 feet as she was being hoisted up towards the roof of the stage on a wire for a battle scene in the show.

It is believed to be the first fatality in the history of Cirque du Soleil, the Canadian-based animal-free circus troupe known for its offbeat performances which have toured around the world.

"(The artist) was being hoisted up the side of the stage and then just plummeted down," witness Dan Mosqueda was quoted as saying by the Las Vegas Sun.

"Initially, a lot of people in the audience thought it was part of the choreographed fight. But you could hear screaming, then groaning, and we could hear a female artist crying from the stage."

Cirque du Soleil founder Guy Laliberte said in a statement posted on Facebook he was devastated by the tragic accident.

"I am heartbroken. I wish to extend my sincerest sympathies to the family. We are all completely devastated with this news. Sassoon was an artist with the original cast of Ka since 2006 and has been an integral part of our Cirque du Soleil tight family," Laliberte said, referring to Guyard by her stage name.

"We are reminded, with great humility and respect, how extraordinary our artists are each and every night. Our focus now is to support each other as a family."

A statement from Cirque du Soleil said the organization was working with authorities in Las Vegas to determine how the accident occurred.

"The entire Cirque du Soleil family is deeply saddened by the accidental death of Sarah (Sassoon) Guyard, artist on the production Ka, that happened on Saturday, June 29th, in Las Vegas," the statement said.

"We have been working with the appropriate authorities and have offered our full cooperation," it added.

Performances of Ka have been cancelled until further notice, the statement said.