Three men have been injured after they challenged a suspected shoplifter who then sprayed them with a noxious substance.
The victims were taken to hospital after emergency services were called to Westbourne Grove in Notting Hill, west London, at 14:09 BST
Scotland Yard said a "noxious irritant" had been used in the attack.
The men's injuries are not thought to be life-threatening or life-changing and no arrests have been made.
The Met Police said the three victims had approached the man who they believed had been stealing from the shop.
The owner of a nearby fruit and veg shop said the attacker began "throwing things around" and "sprayed people's faces".
Another witness, who works in a nearby frozen yoghurt shop, said police officers were "pouring water on people's faces".
London Fire Brigade sent crews from Kensington and Paddington fire stations, while the London Ambulance Service also sent multiple resources - including a hazardous area response team.
Detectives are working to establish what the substance is.