Six people were believed to be injured after being sprayed by a noxious substance in a shopping center in east London on Saturday, police said.
The injuries are believed to have occurred at different locations at the Westfield Shopping Center in Stratford, police said. One man has been arrested, but police said they believed a group of men are responsible.
The incident is not believed to be terror-related, police said.
At least five patients were treated at the scene, and three of them were taken to hospital, Paul Gibson of the London Ambulance Service told BBC News.
Witnesses at the scene told the BBC News that an argument had broken out among a group of people.
A man who gave his name as Hossen, an assistant manager at Burger King, told BBC News that a victim had run into the fast-food chain to "wash acid off his face".