Firefighters dealt with an incident following a road traffic collision on Southend Arterial Road in Romford.
A vehicle collided with a gas main. A man was removed from the vehicle and was taken to hospital by London Ambulance Service crews.
Assistant Commissioner Patrick Goulbourne said: “Due to the nature of the collision, impact to the road network and the impact on the wider community, the Brigade declared a major incident which has now been stood down.
"Crews worked with partners to make the scene safe as quickly as possible.
“There were road closures in place which caused severe congestion and we urged people to avoid the area.”
Properties in the surrounding area were evacuated and a 200m safety cordon was put in place as a precaution.
The Brigade was called at 1815 and the incident was over for firefighters by 2319. Fire crews from Harold Hill, Bexley, East Ham and surrounding fire stations attended the scene.