The attack occurred on Lessar Avenue near Clapham Common at around 7:25 pm, according to Lambeth Police.
Detective Superintendent Alexander Castle said a mother and two young children were taken to the hospital after a male suspect allegedly threw a corrosive substance at them. Authorities believe the substance was acid but are still awaiting results.
Three adults who rushed to aid the family were also transported to the hospital with unspecified injuries. In addition, three responding police officers suffered minor injuries at the scene and are being treated at the hospital, according to Detective Castle.
"While tests are ongoing to determine what the substance is, at this stage we believe it to be a corrosive substance," said Castle, according to the Telegraph.
"A man was seen fleeing the scene. We are drawing on resources from across the Met to apprehend this individual and work is ongoing to determine what has led to this awful incident," added Castle.
The suspect remains at large and police did not specify the severity of injuries. The detective said that they will provide an update on the conditions of the injured people as soon as possible.
"The National Police Air Service are assisting us. Any members of the public who can help us with information or material should call 999 immediately ref CAD 7790/31 Jan," police said.
