Fifteen fire engines and over 100 firefighters and officers have responded to a fire in Knightsbridge, central London, London Fire Brigade said.
Thick plumes of black smoke could be seen billowing into the sky from the luxury Mandarin Oriental hotel on Wednesday afternoon.
The fire brigade said the cause of the blaze was not yet known, but confirmed 35 calls had been made to the fire.
London Fire Brigade confirmed said: "Fifteen fire engines and 97 firefighters and officers have been called to a visible fire in William Street in Knightsbridge.
That figure later rose to 120 firefighters.
"The Brigade's 999 control officers have taken more than 35 calls to the fire, which is producing a lot of smoke.
"The Brigade was called at 3.55pm. Fire crews from Chelsea, Kensington, Hammersmith, Battersea and other surrounding fire stations are at the scene."
This is a developing story.