The chemical, normally used in plastic manufacturing, ran down a stormwater drain and out into the Manukau Harbour.
Auckland Council manager of environmental health Mervyn Chetty said the risk of health effects is low, but dogs and people should keep out of the harbour.
He said the clean-up should be completed by Monday, but in the meantime, people should be on alert for an acrid, fruity odour.
In the wake of the spill, householder and workers in the Penrose and Onehunga industrial area were warned to keep windows and doors shut.
Yesterday about 100 eels were found dead in a stream in the area.
Auckland Council said an investigation into how the incident happened is continuing.