Six fire engines and 35 firefighters and officers are currently attending a fire at a vets with a flat above it on Cambridge Road in Bromley.
Two people were treated at the scene before being taken to hospital suffering from smoke inhalation by the London Ambulance Service.
Five members of staff and all of the animals have been safely evacuated from the building.
The fire is affecting the roof of the veterinary surgery and part of the first floor is alight. Most of the roof of an adjacent house is also alight.
Station Manager Lee Sparks who is at the scene, said: “The roof is well alight and crews are using an aerial ladder platform to try and bring the fire under control.”
Firefighters from Woodside, Lee Green, New Cross, Lewisham and Sidcup fire stations are at the scene.
The Brigade was called at 1313. The cause of the fire is not known at this stage.