Media captionParent of Justin Bieber fan: "To me it is just utter contempt for his fans"
Singer Justin Bieber has said sorry to fans for a late start at his sold out concert at London's O2 Arena.
Writing on Twitter, he blamed "technical issues" for the 49-minute delay on Monday.
"Last night I was scheduled after 3 opening acts to go on stage at 935 not 830 but because of some technical issues I got on at 10:10," he wrote.
"There is no excuse and I apologise for anyone we upset. However it was great show and I'm proud of that."
Initial reports suggested he was almost two hours late on stage.
"I never have any intent to upset or let anyone down. And I'm not okay with things being exaggerated. Once again sorry for anyone upset," added the singer.
A spokesman for The O2 said promoters have been asked to explain why the pop star was late.
He confirmed refunds would be dealt with by the arena's operators, AEG Live "on a case by case basis dependent on the credibility of the claim".
HOW WILL JUSTIN'S LATE SHOW AFFECT 'BRAND BIEBER'?
Obviously those people who were there last night are going to have negative feelings towards him, given they had spent a lot of money for tickets and they were waiting a long time for him to turn up - and, in some cases, having to leave before he had even started in order to get their last trains home.
But you have to put it into context. We are talking about one or two shows here from an artist who has performed many shows in the last few years. The significant thing will be how Bieber's team deal with this situation.
There was confusion over what time Bieber was due on stage, with The O2 saying on Tuesday the 19-year-old was scheduled to appear at 21:30, following performances from three support acts, including Carly Rae Jepsen and Cody Simpson.
Fans who began arriving for the sold-out concert when the doors opened at 18:30 GMT said on Twitter there were boos from some people in the crowd almost an hour before he emerged.
Louise Collier from Bexleyheath, Kent, said she expected Bieber to start "somewhere between 8pm and 9pm".
"I knew there were a couple of support acts, so from experience, I expected him to be on stage about 9pm," she said.
Mrs Collier took her daughter to the concert for her birthday. She paid £120 for two tickets but said: "There's no way I would have let her go if I knew it was going to be that late."
"She enjoyed it - but a definite shine has been taken off it and if she wants to see him again, she will have to save up and pay for the tickets herself as I won't be paying.
"My daughter was very disappointed as he played a much shorter set and there was obviously an awful lot of songs missing. I think he was on stage for only an hour."
It is not the first time Bieber has appeared late on stage - he kept fans in Nottingham waiting for an hour on Saturday, eventually beginning his show at 22:00 and ending at 23:40.
As fans waited for Bieber to arrive on stage at The O2 on Monday, the arena's house disc jockey played a selection of songs.
Speaking outside the venue, one fan said: "They were playing Michael Jackson song, after song, after song - it was so annoying.
"Everyone was on edge and as more time passed, everyone was getting more worried and booing."
Richard Hayward from Folkestone, Kent, took his 15-year-old daughter and her two friends, but they only saw 15 minutes of Bieber's performance as they had to get the last train back to Swindon.
"When I found my daughter she was completely distraught in floods of tears," he said. "One of her friends was exactly the same. The other was just livid with anger.
"Irrespective of what's gone on she still sees herself as his number one fan. If we'd known at the outset that it was going to finish at that time there's no way we could have gone," he added.
Bieber will perform three more concerts at The O2, including Tuesday 5, Thursday 7 and Friday 8 March.
Earlier, the O2 replied to a fan on Twitter saying the venue would be doing "everything within our power to ensure Justin makes it on stage at the right time" for Tuesday's performance.
It later added: "We have been informed by the @justinbieber team that he is scheduled to go on stage at 9pm tonight. Support acts start from 7pm."
Bieber performed several shows in Manchester and Liverpool in recent weeks which all ran to schedule.