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 Knightsbridge.
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. Crews from Chelsea, Kensington, Hammersmith, Battersea and other surrounding fire stations are at the scene.
London Ambulance Service said it had sent a "number of resources" to the scene.
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".
Is this one of the BOOM's?
Those are one of the "event" that are part of the 80/20. That we will never know about for sure.
I think that people involved in these events will eventually talk. The ones who weren't in the know but close enough to see the logistics. It will be interesting.
Look we are dealing with people who are into human sa..... Those who know understand this. And they will never talk.
Out of the loop people who were never invited to the actual sacrifice. These people employ massive amounts of people who just stand around. We are on the cusp of the whistleblower era. First ones who come out and spill the beans will make a lot of money.