West and his wife Kim Kardashian were among the celebrity guests in the New York audience on Monday night for The Cher Show.

But midway through the musical about the career of the singer and actress, cast member Jarrod Spector, who plays Cher's late husband Sonny Bono, tweeted directly to the rapper.

"Hey (at)kanyewest so cool that you’re here at (at)TheCherShow! If you look up from your cell phone you'll see we’re doing a show up here," Spector tweeted. 

"It's opening night. Kind of a big deal for us. Thanks so much."

West apologised in a Twitter response for his "lack of etiquette".

"The dynamics of Cher and Sonny’s relationship made Kim and I grab each other’s hand and sing 'I got you babe'. Please pardon my lack of etiquette. We have so much appreciation for the energy you guys put into making this masterpiece," the Jesus Walks singer tweeted.

Cher, 72, joined the cast on stage at the end of the show for a rendition of one of her biggest hits, If I Could Turn Back Time.

The show contains 35 of the singer's hits and traces her life from its humble beginnings through her 50-year career and life as a superstar.

Cher said on the red carpet that she felt emotional just watching the show.

"Sometimes it's joyous, sometimes it's too close to the bone... And you know, I have Kleenex," she said.

Australian Associated Press