Asked whether she'd consider portraying Fiona on stage, she said: "No. Absolutely not. What they do up there ... is, to me, impossible. It's wonderful, though. They've done such a great job. They worked really hard, and it really pays off."
Tony-winning actress Sutton Foster plays Fiona in "Shrek the Musical," which began preview performances last month at the Broadway Theatre. Actor Brian d'Arcy James portrays the titular smelly green ogre who lives in a swamp and falls for Fiona.
"It's hilarious," said Diaz, sporting a white Bill Blass dress, black Dior coat and bright red lips. "There's so many laughs. ... It's great to see all the actors playing it together, because when we do it for the animated (films), we never see each other. We don't work together."
Diaz reprises her voice role in the fourth "Shrek" film, slated for release in 2010. Mike Myers and Eddie Murphy will return as Shrek and Donkey, respectively.
Joining Diaz at Sunday's performance were America Ferrera, Joan Rivers, Rosie Perez, Kathie Lee Gifford, Hoda Kotb, Phylicia Rashad, and Ben Stiller and his wife, actress Christine Taylor.
"We are 'Shrek' fans at our house," Stiller said while Taylor posed for photographs on the red carpet. "And we're going to go check out the musical and let the kids know if it's suitable for children."
Rivers bantered with Gifford and Kotb, who co-host the fourth hour of NBC's "Today Show." When Gifford asked for Rivers' favorite "Shrek" character, Rivers responded: "Oh yeah, like I care! We're all grown-ups! I'm thrilled to be here."
Rivers, who had a cameo in 2004's "Shrek 2," cracked: "I'm part of the family. But I'm not hardly, like, excited to see 'Shrek' (onstage)."