Brad Pitt joked about how he has become a "zombie expert" as he showed footage of his new film World War Z at CinemaCon.

Before a 15-minute preview of the movie was shown, the Hollywood actor - who plays a UN employee who tries to stop a zombie outbreak in Marc Forster's apocalyptic horror - admitted he wanted to make something his three sons could enjoy, reported Variety.

"Five years ago, I knew nothing about zombies. Now I'm something of an expert," he told the crowd at Caesar's Palace in Las Vegas.

The 49-year-old added: "I think you are going to like this as much as my boys will."

Sneak peeks of Star Trek Into Darkness and Pain And Gain - introduced by director Michael Bay - were also shown at the film convention, which runs until April 18.

Chris Pine, who reprises his role as Captain Kirk, was joined by Star Trek co-stars Zachary Quinto, John Cho and Alice Eve, and writer-producer Damon Lindelof.

Chris teased that his character will be more vulnerable than he was in the 2009 film, saying: "In the first film, Kirk got the chair a bit too prematurely. In this instalment, we see Kirk earn the chair."

Both Zachary (Spock) and John (Sulu) admitted they were "sobered" about promoting their new film, just hours after the Boston Marathon bomb blasts.

Zachary, who starred in a theatrical production of The Glass Menagerie in Boston, said: "I just lived in Boston the last three months. I was horrified. It's just unfathomable."

John added: "This is part of the job for us. But it was a weird feeling. I'm just going to say that. It's so sobering."