VIN DIESEL bursts into a quiet hotel room, his team in tow, brandishing a speaker attached to his mobile phone.

The Hollywood action man then selects a disco track to blast out the 1974 Redbone tune Come And Get Your Love and proceeds to shake his gym-honed body to the beat, as an assistant films proceedings for the star's "archive".

It's not exactly the entrance you'd expect from the Hollywood tough guy, known for portraying gravelly-voiced, burly bruisers in films such as xXx and the Fast & Furious franchise.

But then, Diesel's latest acting gig couldn't be further removed from the usual 'hard man' roles, which have helped earn his Facebook page almost 82 million 'likes'.

The 47-year-old former bouncer provides the voice for a giant tree creature named Groot in the Marvel action movie Guardians Of The Galaxy (which features the Redbone song on its soundtrack).

Groot and his fellow Guardians, a quintet of intergalactic misfits must ensure a potentially destructive orb doesn't fall into the hands of a power-hungry villain called Ronan.

Loyal, kind and mighty, Diesel's character takes the notion of a strong, silent type to the extreme - he can only communicate using three words ("I am Groot") and a series of grunts.

"It's the most innocent character I've ever played, clearly, which is why I've kind of been so silly," Diesel says when he settles down post-dancing, his sizeable muscles packed into a dark T-shirt and combats.

"I'm not talking about heavy issues that I'm usually talking about with the movies I make... I get to have fun!"

It's been a difficult few months for the New York-born actor, whose friend and Fast & Furious co-star, Paul Walker, was killed in a car crash during a break from shooting the hit franchise's seventh film last November.

A hush descends on the room as Diesel discusses finishing the film without his friend, whose brothers were drafted in to help complete his unfinished scenes.

"It was the hardest film to do - and blessed, because there was such a sense of family and coming back. But surreal," he says, looking downwards as he speaks.

Voicing the role of Groot shortly after the tragedy was a "very healthy and therapeutic thing to do" for the actor.

"When we deal with death, our appreciation for life is represented in so many ways," he adds. "We appreciate everything that's alive, the very trees in our backyard. And this character celebrates life, in so many ways."

Diesel, who has two children with his model girlfriend Paloma Jimenez, says it was his three-year-old son who encouraged him to play Groot.

"Someone in my office said: 'What the hell are you going to play a tree for?'

"I went to the living room and showed my children the concept art of all the characters and said, 'Which character do you think Marvel wants Daddy to play?' and my son pointed to the tree."

He continues: "Jump cut to him seeing the movie with me... As I was riding home, my son was looking out the window at trees and he said: 'Daddy, look, it's your brothers and sisters'."

Director and co-writer James Gunn supplied Diesel with a special script for his stints in the voice-over booth.

"With every 'I am Groot', on the right hand side of the page was a paragraph or a sentence of what Groot was really saying," the actor explains.

"So that was how I was trying to get meaning into each 'I am Groot', and make each of them different."

As Diesel's 'people' start to hurry him along, the star announces: "I am going to let you be Groot."

He proceeds to pick up his phone again and urge those present to start shaking their shoulders, whooping and cheering his encouragement as an upbeat song plays out.

"That felt good and you know it! You feel liberated, a better person.

"At the end of the day," he adds, his voice becoming a deep growl: "WE are Groot."