The London Ambulance Service has responded to the scene
Emergency services responded to the scene on Warburton Road at 1.09am BST.
Witness Phie McKenzie wrote: "Scary scenes in Hackney tonight, we have heard reports of chemical burns of people in the building here."
The London Ambulance Service said: “We sent multiple resources to the scene including paramedics in cars, ambulance crews, a number of officers, an advanced paramedic and our hazardous area resource team.”
No reports have yet emerged about what the burning substance was, but it is understood two other people later presented themselves with similar injuries at an east London hospital.
The incident is believed to have sparked the evacuation of the venue where around 600 revellers had been at an event.
Around 200 reportedly had left the premises before the arrival of emergency services, with a further 400 evacuated from the building believed to be a club.
Emergency services responded to the scene sparking an evacuation of the building
A Metropolitan Police spokesman said the substance has not be identified and an investigation is ongoing.
Another spokesman added: "Police were called to a licensed premises in Sidworth Street, Dalston, at approximately 1.10am on 17 April, after members of the public complained of a noxious substance.
"London Fire Brigade and London Ambulance Service were called to the scene.
"Nine 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 victims' injuries are non-life threatening."
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More to follow.