London Fire Brigade (LFB) confirmed that around 60 firefighters attended the blaze on Albemarle Street, which broke out at just after 4pm.
According to the LFB’s initial report, the fire was brought under control by 6:29pm.
In a statement on its website Gymkhana confirmed that the fire service was quick to respond, and that all staff and diners were safe.
“Currently Gymkhana is not taking further reservations,” the restaurant added.
“All existing bookings are being retrospectively rescheduled and re-booked at other JKS Restaurants and partner venues to minimise further disruption.”
LFB is currently investigating the cause of the fire, which damaged half of the restaurant’s downstairs space and destroyed its ventilation system.
Gymkhana, which is owned by JKS Restaurants, opened in 2013 and was awarded a Michelin star in 2014.
JKS Restaurants' portfolio also includes Trishna, Hoppers, Brigadiers and delivery brand Motu Indian Kitchen.
The group also backs restaurants including Bubbledogs, Bao and Sabor.