Zac Efron happy to slim down for new movie

US actor Zac Efron smiles as he is interviewed, at the French Premiere of We Are Your Friends, in Lomme, near Lille, northern France, Wednesday, Aug. 12, 2015. (AP Photo/Jacques Brinon)

Hollywood heart-throb Zac Efron has revealed how it was "fun" slimming down and being less buff for his new film, We Are Your Friends.

The Bad Neighbours star had to shed some kilograms, appear less muscular and lose his golden tan to play an aspiring DJ in the drama, which marks the directorial debut of Max Joseph.

"That was kinda fun. Everything seems to be bulking up, you have to bulk up for a part, you know? It was fun to go backwards and play a DJ and more skinny, svelte guy," he said at the film's European premiere at the Ritzy Picturehouse cinema in Brixton, south London.

The 27-year-old actor said he embarked on an exercise regime so he could lose weight gradually.

"Max and I talked about that early on. I guess to be more authentic, I was running a lot so I just let it happen naturally," Efron added.

Efron, who is best known for starring in Disney's High School Musical movies, also joked about muscling out Dwayne 'The Rock' Johnson in the upcoming Baywatch film.

The pair have signed on to don the red shorts and practice their slow-motion running for the big-screen adaptation of the 90s TV series, which starred David Hasselhoff and Pamela Anderson.

Asked if he would be bulking up again, he said: "I don't know, I'm not sure.

"I'm just going to be swimming - I've got to outswim The Rock. I'm pretty excited, I'm very excited."

Hundreds of fans waited for hours in the rain outside the cinema for Efron, who was joined by his co-star Emily Ratajkowski and film maker Joseph.

Despite playing a DJ in the film, Efron, who received training by a professional electronic dance producer, admitted his own musical skills could do with some work.

"I cannot produce anything but I can play a little set. We are all great iPhone DJs," he said.

We Are Your Friends follows Efron's character as he questions life and friendships through his quest to find the one track that will give him a hit.

"This has been one of the best experiences of my life. This movie is really for our generation - I don't know what it is that I identified so strongly with," the actor explained.

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