New High School film 'under way'

High School Musical became an international hit

Work on High School Musical 4 has begun even though the third instalment is months away from opening in cinemas.

Disney Channel president Rich Ross confirmed to the Hollywood Reporter that writing was underway.

But it is not known whether the film's biggest stars Zac Efron, Ashley Tisdale and Vanessa Hudgens will return for the franchise's fourth outing.

Mr Ross said: "Are we going to have all the cast back? Probably not... Will we have some of them? I hope so."

While High School Musical 3: Senior Year will be shown on the big screen, Mr Ross said High School Musical 4 was "likely" to be a TV movie.

The first High School Musical took the US by storm when it debuted on the Disney channel in January 2006. It went on to become a worldwide hit.

The second TV movie shattered cable TV records last summer with a premiere watched by 18.6m in the US.

Filming on part three begins in Utah later this month. The movie is due to hit cinemas in October.