Three people are believed to have been injured in a "noxious substance" attack in west London, Scotland Yard has said.
A spokesman said: "Police were called at approximately 2.09pm to reports of a noxious substance attack on Westbourne Grove.
"Officers are in attendance along with the London Ambulance Service and the London Fire Brigade."
It is "believed there are three victims" at this stage while officers are working to determine what the substance is, the spokesman added.
No arrests have been made.
The owner of a nearby fruit and veg shop said: "We just know there was one crazy man throwing things around - about 35 or 40 years old.
"He sprayed people's faces."