LONDON (AP) — Four people were hospitalized in critical condition on Friday after a suspected crush at a London concert venue.

Police said eight people were taken to hospitals after being caught in a crowd of people trying to get into the O2 Brixton Academy, where Nigerian singer Asake was performing. Two other injured people were treated at the scene.

Police said emergency services were called Thursday night after “a large crowd attempted to gain entry without tickets.” Video from outside the venue shows scores of people pushing to get in.

The Metropolitan Police force said officers, ambulance crews and firefighters arrived and found “a number of people with injuries believed to have been caused by crushing.”

The force said it would hold a thorough investigation into what happened and how officers treated the crowd.

Metropolitan Police Gold Commander Ade Adelekan said officers who use force “know they have to be accountable for their actions.” He said officers’ body-worn video footage would be studied as part of a probe into the incident.

“This is an extremely upsetting incident which has left four people critically ill in hospital. My thoughts and prayers are with them and their families,” he said. “A police investigation has been launched, and it will be as thorough and as forensic as necessary to establish exactly what happened last night.”