According to Sky News, around 120 firefighters are tackling a blaze at a five-star hotel in central London.
Huge plumes of smoke were seen coming from the historic Mandarin Oriental building in Knightsbridge.
London Fire Brigade said it was called shortly before 4pm and the cause of the flames was not yet known.
Twenty fire engines are at the scene including crews from Chelsea, Kensington, Hammersmith and Battersea.
London Ambulance Service said it had sent a “number of resources” to the incident including its hazardous area response team.
Staff from the Mandarin Oriental Hotel were evacuated to Hyde Park where they were being given bottles of water.
One worker, who asked not to be named, said: “The fire alarm started and everybody was told to get outside.
“Everything’s fine but we don’t know how it started yet.”
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.”
Witness reported that the fire could be seen in the middle floors of the 12-storey building, while a tradesman working at the hotel said he “could see orange flames on the roof”.
Graham Heels, who works near the hotel, told Sky News: “There was a lot of smoke billowing from the roof, thick black smoke, and debris floating up into the air.”
The 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 including Dinner by Heston Blumenthal.
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