At least 12 people suffered burn injuries caused by a suspected noxious chemical in a Dalston bar in east London on Monday (17 April).
Emergency services rescued some 400 people from Mangle E8 night club in Sidworth Street, London Fields after the police were alerted at around 1.10am BST.
Around 600 people attended an event on Sunday night at the night club and nearly 400 were still in the building when the suspected noxious substance led to chemical burns to some attendees.
The London Ambulance Service said that it had dispatched a number of ambulance crews and a hazardous area response team to the venue soon after receiving complaints.
It added that 10 people were treated for minor burns at the scene before being rushed to a nearby hospital. Two other people also visited a hospital later with chemical burns.
"Police were called to a licensed premises in Sidworth Street, Dalston, at approximately 1.10hrs on 17 April, after members of the public complained of a noxious substance," a Met police statement said, according to Sky News.
"London Fire Brigade and London Ambulance Service were called to the scene. Ten people have been treated for minor burns at the scene and taken to east London hospitals by LAS.
"Another two people presented themselves at an east London hospital with similar injuries. All injuries to victims are non-life threatening," the statement added.
A Scotland Yard spokesman told the BBC that police have made no arrests, but are investigating the case. The area has reportedly been cordoned off for investigation.
An eye-witness, Phie McKenzie, tweeted: "Scary scenes tonight, we have heard reports of chemical burns of people in the building here". She also posted pictures of the area showing heavy police presence outside the building.