A suspected acid attack has been reported near the royal residence of Kensington Palace in central London.
Pictures posted on social media showed a man being hosed down by firefighters.
Reports claim the victim is a 17-year-old cyclist.
A spokesman for the Metropolitan Police said: "Police were called at 10:09 hours today, Tuesday 8 August to reports a person being sprayed with an unknown substance in The Broadway, Kensington Gardens."
Many acid attacks have recently taken place, particularly in London, and during the course of the last year the amount of acid attacks has risen by 65%.
Several people were attacked with acid on July 13 in Hackney, Stoke Newington, and Islington and police claimed those incidents were linked.
There have also been a number of other attacks elsewhere in the country, most recently in the Cheshire village of Lymm this week.