Zac Efron's averted an embarassing wardrobe malfunction at the weekend when he had to grab on his pants to stop them falling down.

The High School Musical star was forced to take immediate action as his baggy jeans started to creep down his backside to reveal his white undies and a hint of pert rear.

Zac's flash occured in the presence of girlfriend Vanessa Hudgens and HSM co-star Ashley Tisdale, both of whom seemed oblivious to the actor's falling pants.

Zac and Vanessa's love story in pictures

Take a peek at Zac's undies below