Residents were injured after a chemical substance was sprayed inside a block of flats during a fight.
Police were called to reports of a disturbance at flats on Beckenham Road, south London at 7.20am on Thursday.
Detectives discovered that a chemical substance had been sprayed in the communal area.
A Scotland Yard spokesman said: “A small number of people were treated at the scene.”
Five people were arrested on suspicion of affray and have been remanded in custody.