At least 12 people suffered burns during a suspected acid attack at a club in east London.
Hundreds of revellers were evacuated from Mangle E8 in Sidworth Street, Dalston, after police were called at about 01:10 BST.
London Fire Brigade said a “strong acidic” unknown corrosive substance was thrown inside the venue.
Police said 10 of those affected were taken to hospital by ambulance, while a further two sought treatment at A&E.
Their injuries are non life-threatening.
A London Fire Brigade spokesperson said: “The only information that we have is that it was an unknown corrosive substance thrown within the nightclub.
“It was identified by a PH paper test as a strong acidic substance.”
It is understood about 600 people had been attending an event at the nightclub before it was evacuated.
A Scotland Yard spokesman said the 10 people were treated for minor burns at the scene before being taken to hospital.
No arrests have been made and officers are continuing to investigate, he added.
Witness Phie McKenzie tweeted: “Scary scenes tonight, we have heard reports of chemical burns of people in the building here”.
London Ambulance Service said it sent a number of ambulance crews and a hazardous area response team to the venue.