Update, August 21, 3.30pm:
A burst water main in O'Callaghans Parade, Horsham, will cause traffic disruption until at least late Thursday afternoon.
Southbound traffic will continue to be blocked at Sloss Street, and northbound traffic will experience detours, with turns into Urquhart Street blocked.
The Baker Street intersection with O'Callaghans Parade will also be partially blocked.
Traffic is advised to take alternative routes, including Wilson Street or Hamilton Street
Update, August 21, 9am:
Horsham's O'Callaghan's Parade is still closed in parts after a burst water main on Tuesday night.
Horsham Rural City technical services director John Martin said O'Callagan's Parade would be closed to southbound traffic for the remainder of the day.
"Turning right from O'Callagan's Parade into Urquhart Street will be closed for a fair while," he said.
Mr Martin said vehicles were still able to travel north on O'Callagan's Parade, but traffic could be interrupted at times throughout the day as machinery moved through.
"Baker Street is also open, but you can't turn right into O'Callagan's Parade from it," he said.
Mr Martin encouraged people to avoid the area if possible.
"People should used Hamilton and Wilson streets if they can," he said.
"It is still possible to get through - people will still be able to go to VicRoads or get their chicken pack for lunch if they want to, they just might have to detour around the works."
A GWMWater spokeswoman said water supply had returned to normal.
Authorities say it is not yet known how long a section of O'Callaghan's Parade will be shut for, after a water main burst on Tuesday night.
A burst at the traffic island near the intersection with Urquhart Street before 6pm has sent water and sand cascading across the road.
A GWMWater spokeswoman said crews were still investigating which pipe was impacted.
"The road will remain closed until they investigate the source of the break," she said.
Traffic is being diverted via McPherson Street/Western Highway, with the road closed between the turbo roundabout and Hamilton Street.
Sergeant Adam Bronca said VicRoads had been notified.
"They're going to have to rebuild the whole road I'm assuming," he said. "We know it happens every now and then with our good ground movement."
GWM Water and Horsham Rural City Council representatives are also on scene.
More to come.