The world premiere of the screen version of Chicago, the blockbusting stage musical was held in London on Sunday.

But the prestigious event was without one of its leading ladies - a pregnant Catherine Zeta Jones did not fly from her Los Angeles home to attend alongside Richard Gere and Bridget Jones' star Renee Zellweger.

Ahead of the film's debut in Leicester Square, Zellweger, who plays seductive murderess Roxie Hart, spoke of her amazement at the Welsh actress's singing and dancing ability.

It's not just singing and dancing, she belts it out. Renee Zellweger

She said she was "staggered" by the ability Zeta Jones - who got her first break in the West End production of 42nd Street aged 17 - showed on set.

"I had heard that Catherine could sing and dance. People would say 'You're not going to believe it'.

"Well, I walk in on my first day and she's in a lift singing All That Jazz and I was just dumbfounded," admitted Zellweger.

"My jaw dropped to the floor. I didn't speak for 30 minutes. Just sat in the corner in awe and watched.

"It's not just singing and dancing, she belts it out.

"I'm like a little field mouse compared to her. Squeak, squeak, squeak.

Zeta Jones as nightclub singer Velma Kelley

"And the movement - I would stand a few steps back and watch her. I was learning, basically, to dance by watching."

Zeta Jones was reported to have found her previous experience in musicals very useful during the intense training period with vocal coaches and dance instructors before filming began.

She plays the role of Velma Kelley, a sensational nightclub singer who ends up on murderers' row when she shoots her adulterous husband.

She hires lawyer Billy Flynn, played by Richard Gere, a slick and sleazy lawyer, who also takes on the case of Roxie Hart, imprisoned alongside Kelley for a similar crime of passion.

The two women vie with one another as they strive to become the most infamous and celebrated woman in the city of Chicago.

Star Richard Gere: "Easy on the eye"

Zeta Jones' singing was so good in the film that producers reportedly dropped the idea of getting Janet Jackson to record the end version of All That Jazz and used hers instead.

Actress Claire Sweeney, who has starred in the West End version of the musical, had a sneak preview of the film ahead of Sunday's screening.

She said: "I thought it was amazing. It was very, very good, really original.

"I think a lot of people will be surprised at Catherine's ability - she's truly great.

"She's very sensual, very sexy, very strong, just a brilliant singer and dancer.

"And Renee Zellweger has a very knowing twinkle.

"Richard Gere is excellent: fine voice and really great singer. We all know he's a very good actor and he's easy on the eye."