Great South Rd in Auckland's Penrose has been re-opened to one lane in each direction between Station Rd and Penrose Rd.
That section of Great South Rd had been closed because of a burst water main.
Traffic has been heavy in the area and motorists are being urged to avoid it.
The NZ Traffic Agency reported the partial re-opening at 5pm.
Auckland Transport too is urging motorists to avoid the area or face long delays.
The underground water main broke earlier this afternoon and began fountaining water up through the surface.
Watercare Services said it had a crew on site repairing the 300mm-diameter pipe.
Police said the road was closed between Penrose and Station Rds. They asked motorists to avoid the area.
"Contractors are working to resolve the issue and advise the situation may
take some time," the police said.
Auckland Transport said some bus services, including school buses, were affected.
Watercare said the road had been closed because the pipe break had caused a pothole to form
"The water has been turned off. This is not causing any water outages although it is possibly causing low water pressure in some streets.
"We do not know the cause of the break at this stage. We expect it will take a number of hours to repair."
Fire and Emergency NZ said earlier that two fire engines were at the scene to ensure water did not get into buildings.
"We are waiting for Watercare to get it under control, if they haven't already," a spokesman said.
He said firefighters "came across" the flooding at 1.30pm
"It's quite substantial flooding from a broken water main."
"[The water] is encroaching on buildings. We haven't been told it's got into any buildings."
Meanwhile, in separate road incident, the NZ Transport Agency said at 6.30pm that on the Southwestern Motorway northbound a crash in the shoulder after Walmsley Rd was expected to cause some delays.
Earlier, the agency said that on the Southern Motorway southbound there was a breakdown in the shoulder after the Princes St offramp.
A truck breakdown was blocking the left eastbound lane on Lincoln Rd just after the northbound Northwestern Motorway onramp.