"As a precaution, signs at both Matapihi beach and the city centre Tidal Steps will ask people to stay out of the water until testing shows it is safe."
The area remained cordoned off with security guards in place until the clean-up was complete.
The overflow happened during routine maintenance of a valve. A review of maintenance procedures will be held, Burton said.
A council spokeswoman said it was not known how much wastewater overflowed.
The statement issued this afternoon said the council was "working with the local community and hapū to ensure public safety and health and we ask that the public please stay away from this area."
Wastewater from this network has been diverted to Chapel St.