The cause of the fire is not yet known
Around 120 firefighters and 20 fire engines have been called to a blaze at a five-star hotel in central London.
Images on social media showed huge plumes of smoke coming from the Mandarin Oriental in the Knightsbridge area of the British capital.
London Fire Brigade said the cause of the flames was not yet known.
It has taken more than 35 calls about the fire, which is billowing smoke that can be seen widely across the capital.
The fire brigade said it was called at 3.55pm.
London Ambulance Service said it had sent a "number of resources" to the scene.
A hotel spokesman said: "We are aware that there is a fire at Mandarin Oriental Hyde Park, London, and that the fire brigade is at the hotel.
"As the situation is still unfolding, we have no further details to share at this time, but will provide an update soon."
The 12-storey Mandarin Oriental describes itself on its website as "one of London's most celebrated five-star hotels" that "exudes an enticing mix of elegance and luxury".
It has recently completed a multi-million pound renovation and has a number of luxury restaurants.
The Edwardian-style building was first opened as the Hyde Park Hotel in 1902, before it was bought by Mandarin Oriental Hotel Group in 1996.