Thames Water say they are working to bring the flood under control.
"The burst has resulted in severe damage to the road and some flooding to properties in the area. Thames Water representatives and loss adjusters are on site to assess the damage," read a statement.
The flood blocks Maida Vale, which leads into the Edgeware Road - a major artery into central London from the north.
Around 50 basement properties and an underground car park have been affected, with 300 homes losing their water supply.