LONDON - British police said on Monday they had responded to a serious incident at a venue in the northern English city of Manchester where US singer Ariana Grande had been performing.
"Emergency services responding to serious incident at Manchester Arena," Greater Manchester Police said. "Avoid the area."
Witnesses reported hearing a huge bang at the venue, Sky News said on Monday.
A video posted on Twitter showed fans screaming and running inside the venue.
Reuters was not immediately able to verify the reports on social media.
Britain is on its second-highest alert level of "severe" meaning an attack by militants is considered highly likely.