The pipe is a 24 inch trunk main which brings water from the Highdown Resevoir, supplying Goring and Ferring homes.
Southern Water alerted the fire service to the incident at 5.43am. East Preston station sent out one fire engine to pump away excess water and waited until 6.31am for water on the road to subside. Southern Water is in the process of redistributing water from other pipes. It has isolated the burst pipe and stopped the leak.
The eastbound carriageway of the A280 Angmering bypass to the roundabout with Titnore Lane has been closed for six hours.
A Southern Water spokesman, said: “The next step once we have got customers back in supply of water will be to try and identify what caused it. It could be one of a number of things such as ground movement or sudden pressure in the pipes.”
Southern Water have arranged for bottled water to be delivered to the Asda carpark in Ferring for customers without water.
The following schools have closed because of the incident: West Park CofE First and Middle School, Thomas A Becket First School, St Mary’s Catholic Primary School, Palatine School, Oak Grove College, Heene CofE First School and Goring-by-Sea CofE First School.