Some 2,000 people were evacuated from a music venue after a substance, believed to be pepper spray, was released into the audience.
American rapper Lil Pump was performing at Nottingham’s famous Rock City venue when the substance was released.
Twenty people needed medical treatment, though it’s not thought anyone was seriously injured during the incident on Friday night.
The show was called off, with the venue saying “it is incredibly sad when this type of action ruins the event for everyone”.
However, videos taken outside Rock City after the evacuation showed Pump continuing to perform on top of his tour bus in front of a huge crowd.
Rock City said in a statement: “We are working closely with the police investigating the incident from the show last night where a substance believed to be pepper spray was released in the audience.
“We’d like to thank everyone attending the Lil Pump gig for co-operating with our staff so quickly as they worked to evacuate the venue after we stopped the show to ensure public safety.
“Police were on the scene quickly and paramedics treated a number of people for minor injuries.
“Live music is made to bring people together and it is incredibly sad when this type of action ruins the event for everyone.”
Nottinghamshire Police was appealing on Saturday for video footage of the incident.
It said in a statement: “It is usual for events like these to be recorded on mobile phones and cameras, and officers are appealing to anyone with footage in and around the venue at the time of the incident to contact us.
“We are treating this incident extremely seriously, however officers are not considering this to be a terror-related.”
Additional reporting by Press Association.