POP superstar Justin Bieber said he was only human after he snapped and lashed out at a photographer, rounding off a "rough week".
The 19-year-old Canadian singer's latest upset came just hours after a health scare forced him to leave the stage.
He burst out of a vehicle and lunged at the photographer, but was restrained by minders in an incident which was captured by a film cameraman.
Bieber explained in a series of messages on Twitter shortly after the outburst - in which he shouted obscenities on a London street - that his adrenaline was running high and that he "let the paps get the best of me".
He had been hustled into a vehicle by his team after leaving his central London hotel, but he leapt from the van, making threatening comments.
"What did you say? What did you say?" he shouted, before swearing as his minders dragged him back into the vehicle.
The footage has been posted on the Channel 5 News website, after a week which has seen the singer castigated for letting down his school-age fans, then be treated by medics after apparently struggling for breath on stage.
Writing on Twitter shortly after today's incident, he wrote: "Sometimes when people are shoving cameras in your face all day and yelling the worst thing possible at you - well, I'm human. Rough week.
"Not gonna let them get the best of me again. Gonna get focused on this show tonight. Adrenaline is high now. Gonna put it on the stage.
"Only way someone can break you is if you let them," he added.
Charles Murray, a cameraman for 5 News, witnessed the incident and said it was "an angry outburst".
He went on: "He deliberately went out of his way to shove the photographer. The photographer shouted back at him as Bieber got into his car.
"Bieber then decided to get back out of the car and slapped his camera out of the way."
The star, idolised by young fans, was heard to shout: "I'll beat the f*** out of you."
A record company representative did not comment on the outburst by the teenage singer.
Bieber is due to perform another show at the O2 Arena tonight, in a week he would probably prefer to forget.
Last night he quit the stage mid-song complaining of shortness of breath and was checked over by medics.
Earlier today a representative for the singer said he was feeling "under the weather" after his health scare on-stage last night, but was still planning to perform.
He had posted a picture of himself online lying in a hospital bed shortly after the show, during which he had to take a break as he struggled to breathe.
In a message to fans, he said he was "getting better" and trying to figure out what had happened.
It came just days after he angered and disappointed thousands of people by starting his first of four nights at London's O2 arena so late that many had to miss most of the show.
Some of his young devotees were in tears as they left to catch transport home. The following day he apologised for his tardy showing, blaming technical problems.
Bieber also grumbled about the media, saying that reports about his delay had been exaggerated.
During his spell in the UK the singer has been spotted topless in the chilly weather as he went for a late-night celebration.
Last night Bieber was midway through performing the track Beauty And The Beat when he walked off.
His manager, Scooter Braun, told the audience that the singer was seen by a doctor backstage at the venue, who told him not to return to the stage.
Braun told the 20,000-strong crowd: "Justin got very light of breath, the whole show he's been complaining. He's backstage with the EMTs (emergency medical team) and the doctor."
He went on: "You guys need to be patient with us, we're not trying to be disrespectful, we're not trying to get you guys home late, we're truly trying to put on a show for the people who love him."
However, he did resume his performance.
One fan said of Bieber's stage departure, via Twitter: "He literally was so out of breath on stage in the middle of Beauty And The Beat and then went off."
The incident has led to claims it was a publicity stunt to win back the affection of fans after the drubbing he received earlier in the week over his poor time-keeping, for which he eventually apologised, blaming technical problems.
One wrote on Twitter: "Justin Bieber was not sick, it's a publicity stunt to make up for his late show."
Another speculated: "Justin Bieber publicity stunt collapse because he cocked up the other night by being 2 hrs late for his fans. Anything for sympathy?"