The fire broke out at a building in Albemarle Street at about 4.08pm today, Thursday.
Video footage shared on Twitter shows firefighters entering the Michelin-star Gymkhana Indian restaurant with hoses as black smoke pours out.
A spokesperson for London Fire Brigade said: "Half of the ground floor kitchen and half of the ducting from ground floor to roof level is alight.
"Fire crews from Soho, Lambeth, Kensington, Euston, Paddington, Chelsea and Dowgate fire stations are at the scene.
"The cause of the fire is not known at this stage."
Huge plumes of smoke could be seen billowing into the sky behind a tall, glass building in video footage circulated on social media.
The fire brigade said the blaze was under control by 6.30pm and there were no reports of injuries.
The cause of the fire is still under investigation.
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