Thirty fire engines and around 175 firefighters tackled a fire at Forest Gate Police Station.
The mansard roof of the police station was completely destroyed by fire. Three of the Brigade's 32-metre turntable ladders and one of the Brigade's 64-metre turntable ladders were deployed at the scene.
Around 60 people were evacuated from the building before the Brigade arrived. There are no reports of any injuries.
The Brigade was called at 1617, and crews had the fire under control by 2308. Firefighters from Stratford, Leytonstone, Plaistow and surrounding fire stations attended the scene.
The cause of the fire is under investigation.
Assistant Commissioner Pat Goulbourne, the Brigade's Incident Commander, said: "This was a challenging incident for firefighters as the fire was located in the roof of the police station. Crews made extensive use of our 32m and 64m ladders to attack the fire from above, and our drone team was deployed to provided us with a view of the scene as we responded."
"Throughout the incident a concern for our crews was the possibility of the fire spreading to adjacent properties. Thanks to their hard work we were able to prevent that from occurring, and the fire was limited to the police station. Firefighters also conducted operations to ensure that essential police property within the building remained protected from the blaze and moved to a place of safety.
"Our specialist Fire Investigators will now begin to carry out their investigation into the cause of the fire. Due to the scale and nature of the incident, this is may be a protracted investigation."