Ten fire engines and 72 firefighters and officers have been putting out a large fire at an industrial workshop on Ley Street in Ilford.
Half of the first floor and part of the second floor were alight when they were called to the scene just before 10 pm.
Three people had been evacuated from the building before fire crews arrived.
London Ambulance Service crews treated one person from burns who was taken to hospital and two others were assessed for smoke inhalation.
The Brigade was called at 2159 and the fire was under control by 2314.
Firefighters remained there throughout the night damping down pockets of fire.
Fire crews from Ilford and surrounding stations attended the incident.
The cause of the fire is under investigation.