A woman was rushed to hospital and 160 people were evacuated from a leisure centre after chlorine gas was produced.
The London Fire Brigade (LFB) said that the incident at a leisure centre in Highbury Crescent is believed to have been caused by the mixing of chemicals, which produced a chlorine gas.
The brigade was called at 12.06pm and fire crews carried out a sweep of the building and ventilated the property to make the scene safe.
A LFB spokesperson said that fire engines from Homerton and Stoke Newington fire stations and two fire rescue units from Bexley and Lewisham fire stations attended the scene.
The London Ambulance Service (LAS) confirmed that they treated a woman at the scene before taking her to hospital.
A spokesperson said that LAS sent an ambulance crew, an incident response officer, and members of our Hazardous Area Response Team (HART).
Public Health England's website says breathing a small amount of chlorine gas may result in a burning sensation of the eyes and throat, while more substantial exposure may cause coughing or breathing difficulties.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here