Image copyright CBS / WBTV Image caption The cast are seeking up to $1m per episode, according to US media

Work on the eighth series of US sitcom The Big Bang Theory has failed to start on time, as the principal cast members fight for higher salaries.

Stars Jim Parsons, Kaley Cuoco, Kunal Nayyar and Simon Helberg did not return to work for the first day of production on Wednesday.

Negotiations are continuing with studio Warner Bros. Television (WBTV).

The comedy is the most-watched TV show in the US, with an average audience of 23.1 million in 2013-14.

I want them all to be crazy wealthy because nobody deserves it more than this cast Chuck Lorre, Creator, The Big Bang Theory

Earlier this year, the show was extended for a further three series, meaning the show, which centres on a group of high-functioning science "geeks", will now air until at least 2017.

In a statement, WBTV said: "Due to ongoing contract negotiations, production on The Big Bang Theory - which was originally scheduled to begin today - has been postponed."

The move came as a surprise to the studio, which previously said it expected the eighth series to go ahead without a hitch.

The delay affected a "table read" - in which the cast would have run through the script for the comeback episode.

Image copyright AP Image caption Parsons has won three Emmys and a Golden Globe for playing Sheldon Cooper in The Big Bang Theory

According to The Hollywood Reporter, Parsons, Galecki and Cuoco currently earn $325,000 (£190,000) per episode and are seeking up to $1m (£584,000) per show.

Such a deal would make them the highest paid actors on US television - ahead of Ashton Kutcher and Jon Cryer from Two and a Half Men, currently understood to be the most rewarded TV actors.

Both shows were created by Chuck Lorre, who recently said he did not expect the contract dispute to be overly disruptive.

"There are people at Warner Bros. Television and people representing the actors who have done this before," he said earlier this month.

"This will work itself out. I think it's great; I want them all to be crazy wealthy because nobody deserves it more than this cast. It'll work out."

However, salary negotiations on top-rated comedies have turned ugly before. In 2012, several actors on the hit show Modern Family took legal action to have their contracts declared void in a dispute over pay.

After staging a similar walk-out, TV network Fox relented and doubled their salaries.