Ten fire engines and around 70 firefighters were called to flooding on Hornsey Road in Islington.
A 36-inch water main burst causing flooding up to a depth of around 3 feet and two sinkholes. Around 50 properties were damaged by flood water.
Station Commander Matt Brown, who was at the scene, said: "Flood water affected Hornsey Road, Tollington Road and a leisure centre.
"There is severe congestion in the area and multiple road closures are expected to be in place for some time whilst our partners work to carry out repairs. People are urged to avoid the area.
"Firefighters used flood barriers to divert water and assisted two adults and two children to safety. There were no reports of any injuries."
The Brigade's 999 Control Officers took more than 25 calls to the incident.
The Brigade was called at 0701 and the incident was over for firefighters by 1201. Fire crews from Holloway, Islington, Kentish Town, Stoke Newington and surrounding fire stations attended the scene.