Four fire engines and around 25 firefighters were called to a flooding on Avenue Road, Primrose Hill.
A 15 inch water main burst flooding the basement and underground car park of one block of flats to a depth of around one metre.
Two ground floors flats were flooded to a depth of 20cm and firefighters led four people from one of the affected flats to safety. Six cars parked in the basement were damaged by flood water.
The underground car park of an adjacent block of flats was flooded to a depth of 10cm.
Watch Manager Tim Martin, who was at the scene, said: “Fire crews pumped away water using high volume pumps in order to stop more flats from being affected by the flood water. Fire rescue unit crews wearing dry suits searched the basement and thankfully found no one trapped."
The Brigade was called at 2002 and the incident was over for firefighters at 2255. Fire crews from Paddington, Euston, West Hampstead fire stations attended the scene.