Alexander O'Neal had flown in from the US for the Southwark Park concert
A 15-year-old boy has been stabbed in the leg at a festival in London leading to the cancellation of a set by US soul singer Alexander O'Neal.
The day-long event at Southwark Park in Bermondsey was stopped on police advice shortly after 2000 BST just as the singer was due on stage.
The boy, who also suffered facial injuries when he was hit with a bottle, was taken to hospital for treatment.
Several thousand people attended the event as part of Bermondsey Carnival.
Dozens of police were quickly on the scene and a number of young people were interviewed.
No-one has been arrested in connection with the incident.
A Metropolitan Police spokeswoman said the boy's condition was not thought to be life-threatening.
A Southwark Council spokeswoman described the festival as "an enjoyable family event" which had experienced no problems in its previous 12 years.
She said: "We had a big community warden and police presence there but after the incident police advised us to close the event early, which we did."
Alexander O'Neal had flown in from the US to attend the free festival.
The BBC's Paul Rowley said there was booing from some sections of the crowd when the decision to cancel the concert was announced.
Bermondsey MP Simon Hughes said the festival would go ahead next year despite the incident.
"It's very sad that some violence occurred yesterday," he said.
"Young people were clearly misbehaving. We have to make sure that people understand that is unacceptable."
Mr Hughes added: "If we have to next year take additional precautions to make sure everybody going feels safe, then we will do that."