The local police services reported that the hotel was being evacuated and it was not yet known whether there had been any injuries.
Roads in the area have been closed in order to help the emergency services respond to the fire.
"A4 Knightsbridge btwn A3216 Sloane Street (Scotch Corner) + A302 Grosvenor Place (Hyde Park Corner) — Road closed, both ways, while the emergency services respond to a building fire," the local transport service stated on Twitter.
— Arthur (@ArthurWilloughb) June 6, 2018
Earlier, the London Fire Brigade stated that some 20 fire engines and around 120 firefighters and officers were tackling a fire on the roof of a hotel.
"Firefighters are at the scene of a very visible fire in #Knightsbridge We've taken more than 35 calls to the blaze," the London Fire Brigade reported via Twitter.
Mass of smoke over London — anyone know what it is? Fire or explosion? pic.twitter.com/wcI9bmGgUP— Ben Flanagan (@ben_flanagan) June 6, 2018
Fire near Hyde Park London!! pic.twitter.com/LRCQBqWtbw— Libby McBride (@libby_mcbride) June 6, 2018