Three people were injured in a possible “acid attack” in west London.
The incident happened shortly before 11pm on Thursday near Ladbroke Grove Tube station and the Sainsbury’s Local.
London Ambulance Service sent paramedics from its Hazardous Area Response Team.
Police response units and fire crews also raced to the scene.
Two men in their twenties were taken to hospital.
Their injuries were not life-threatening.
A third victim was treated at the scene for a hand injury.
The exact substance used in the attack is not yet believed to have been identified.
The attack happened just days before the Notting Hill Carnival which takes place during the Bank Holiday Weekend.
Police have launched a huge operation, including a string of arrests, to stop more than 300 people who were suspected of possibly planning violence at the world-famous festival from attending it.
In a statement, the Met Police said: “At 22:47hrs on Thursday, 27 August officers were called by the London Ambulance Service to Ladbroke Grove, Notting Hill following reports of an assault involving an unknown substance.
“Police were supported by the London Fire Brigade and British Transport Police.
“Two men in their 20s were taken to hospital and their injuries have since been confirmed as non-life-threatening.
“A third man in his 20s was treated at the scene for a hand injury and did not require further treatment.”
Police enquiries are ongoing and no arrests had yet been made as of lunchtime on Friday.
Scotland Yard added: “Enquiries indicate that this was an isolated incident, with no wider threat to the public.”
People with information about the attack were urged to contact police by calling 101, quoting reference CAD 7927/27AUG, or to do so anonymously via Crimestoppers on 0800 555 111.
A London Ambulance Service spokesperson said: “We were called at 10:41pm yesterday (27 August) to reports of an assault by Ladbroke Grove Underground Station, W10.
“We sent ambulance crews, a paramedic in a fast response car, an incident response officer and paramedics from our Hazardous Area Response Team.
“We treated three patients at the scene and took two to hospital”.
A London Fire Brigade spokesman said: “Firefighters were called to a chemical incident on Ladbroke Grove.
“Two fire engines from North Kensington and Paddington fire stations attended the scene.”
