Anglian Water engineers are working to repair a burst mains pipe in King's Lynn.
The burst was reported at around 4am on Monday, with people in the area experiencing very low pressure or no water at all.
It has affected an area from Central Road, north past River Babingley, and east to Bergen Way.
Anglian Water's engineers are on the scene attempting to get customers their supply back.
They have called it a "complex job" that is taking them longer than expected to fix, though a fix is expected by 8am.
Anglian Water has apologised for the inconvenience.
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