U2 tour: Berlin show cancelled due to Bono voice issues
The Irish band had played a handful of songs when the singer apologised to the crowd, saying: "I think we can't go on. It's not right for you."
Those at the Mercedes-Benz Arena were told there would be a short pause, but were later told the show was over. Bono promised another gig would be arranged.
Some fans said Bono had announced that smoke machines had affected his voice.
"Bono was in great form and great voice prior to the show and we were all looking forward to the second night in Berlin, but after a few songs, he suffered a complete loss of voice, " U2 said in a statement.
"We don't know what has happened and we're taking medical advice," the band added.
It was the second night of the European leg of U2's Experience + Innocence tour, which had kicked off at the same venue on Friday night.
Bono had been singing Red Flag Day when he lost his voice, according to those at the concert.
U2 fan Paul Jones said: "During the fourth song, Red Flag Day, Bono's voice deteriorated massively - he said it was something to do with the smoke that was set off."
He was trying to "soldier on" with the next song, Beautiful Day, when he called a stop to proceedings.
In a video posted by a fan of the Saturday night concert, Bono appeared to be coughing and told fans he was "so sorry".
"I'm sure this is not a big, big problem - but I'm going to have to do something." he said. "If people want to go home, that's fine - we'll play another show for you another time."
Bono said he needed a short break "to find out what's happening" but then did not return.
US actress Ashley Judd was at the concert and said "the crowd so felt for him" as he was "powerless and vulnerable".
One fan said she had travelled from England for the gig for her partner's 50th birthday - and was unlikely to be able to return for a rescheduled date.
She told BBC News that Bono "complained his voice had gone due to smoke from smoke machines". He said he would either cancel or take a short break, but after 30 minutes it was announced the concert was cancelled.
Sharon said: "Very sad it's cancelled but can't be helped if he can't sing. Would have been nice for the band to come out and explain."
It is not yet known when the band will reschedule the gig.