High School Musical star Zac Efron was left shaken during a night out in London with girlfriend Vanessa Hudgens - after he was attacked by a middle-aged man.

The 20-year-old hunk was making his way through a throng of screaming fans as he left the Apollo Theatre with Hudgens on Wednesday after checking out Hollywood star Josh Hartnett's performance in a stage adaptation of Rain Man.

But he was stunned when a man - presumed to be in his late 40s - pushed through Efron's security team and tried to grab the star's hair.

The assailant reportedly screamed and pointed as Efron and Hudgens were hurried away, before security personnel eventually restrained him and moved him away from the area, according to Britain's Daily Mail online.

A source tells the website, "'Some guy was just stood near the door where Zac and Vanessa emerged. He just reached over and grabbed the side of Zac's head. There was no provocation. It all turned into a bit of a mess.

"He was shouting all kinds of things at Zac. Their security team eventually dealt with it. They had to bundle Zac into a car, but at one point it looked as though the man was going to be pushed into it with him."