Two fire engines, two fire rescue units and over 20 firefighters and officers were called to investigate reports of a chemical smell at a disused science lab in Inskip Drive, Hornchurch earlier this afternoon.
A safety cordon was set up and 150 people were evacuated from the area as a precaution.
The Brigade was called at just before 1.30pm and the incident was declared safe just before 5pm on Tuesday afternoon. Crews from Hornchurch and Dagenham attended the scene.
There are no reports of injuries.