Up to seven people have been injured in an explosion and chemical leak at Fonterra's Edendale plant, 40km northeast of Invercargill.
St John Ambulance spokeswoman Alena Lynch said four patients had been transported with minor injuries to Invercargill Hospital. A further three were being treated at the scene, the New Zealand Herald reported.
Ms Lynch said the chemical explosion was caused by Reflux 800, a chlorinate sanitiser.
A Fonterra health and safety spokesman, who did not want to be named, said the accident happened as the chemicals were being unloaded.
He said those at the scene had been treated for gas inhalation.
Two workers had been transported to hospital while a four received attention at the scene, he told the New Zealand Herald.
The spokesman said there was a chemical reaction which resulted in the release of chlorinate gas.
He said a routine investigation would be launched but at the factory was now fully operational.
State Highway One - north and south of the Edendale factory - has been opened again after police set up diversions earlier.
The Department of Labour confirmed it had been told of the explosion and said it was sending investigators from Dunedin.
Police have not yet released details about the blast or its severity.
Fonterra milk tankers unable to access the factory were now slowly filing back into the site, the Otago Daily Times reported from the scene.
On Saturday night a Fonterra worker died after an accident at the company's Whareroa plant in Taranakai.
