Joaquin Phoenix reportedly "stormed out" before a Las Vegas concert after losing his cool with a film crew.

The actor-turned-singer is believed to have been furious when Casey Affleck's camera crew ? who are documenting Phoenix's transition into music ? were late for his sound check at LAVO nightclub last week.

A source said: "He was waiting for Casey Affleck and when the film crew arrived late, Joaquin flipped out. Phoenix yelled at the crew. He then threw a CD on the floor and stormed out."

Phoenix soon regained his composure and returned to the stage to rehearse his set, leaving onlookers unsure if he was genuinely annoyed.

The source added to the New York Post: "He came back five minutes later and did the sound check. Nobody can tell if he is for real or if this is all a big joke."

Later that night, the 34-year-old star surprised onlookers by performing three hip-hop numbers.

During his set, a dishevelled Phoenix ? who was sporting an unkempt beard and long hair ? danced unsteadily and fell into the crowd as he exited the stage.

Phoenix's recent erratic behaviour and bloated appearance has raised concerns for his health.

A source said: "His bizarre behaviour has everyone worried. It's just getting scary."

Phoenix recently admitted numerous people have questioned his desire to pursue a career in the music industry.

He said: "This is my chance to do something straight from the heart and put it out there. Are there people who think it's going to suck? Probably, but I can't worry about that."