Evacuations are underway in the Waikato township of Tūākau after large amounts of an "unknown chemical" entered drains near a water treatment plant.
Fire and Emergency New Zealand said the hazardous substances incident was reported around 4pm.
Residents living in the vicinity of Kowhai St and Matipo Dr have been evacuated, Fire and Emergency said.
"Other people in the area are advised to stay inside with doors and windows closed to avoid possible exposure to fumes. Other members of the public should stay away from the area until further notice.
"The nature and origin of the substance is not yet known."
A resident whose property bordered the evacuation zone told 1News the area smelled strongly of liquefied petroleum gas (LPG).
"They purge the gas lines in Bollard Rd twice a year so thought it was that. It's kinda the same since about 10am."
Fire and Emergency has sought specialist advice from the Queensland Fire Department to assist in identifying the substance and was working with the Waikato District Council and Watercare to develop a plan to flush the drains safely.
Hato Hone St John said it had medical staff at the scene and more were on the way.
"We have one ambulance and one operations manager on scene and another ambulance en route," a spokesperson said. "We cannot give any more information as this is still developing."
Police said they were notified of an incident in Tūākau around 5pm, and were assisting Fire and Emergency New Zealand with evacuations in part of Kowhai St.
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