Five people have been taken to Dunedin Hospital after a workplace accident involving sulphur at the Ravensdown plant.
A police spokeswoman said they were notified at 9.52am.
The spokeswoman said there were reports of injury caused by sulphur burns.
A St John spokesman said two ambulances and a manager were sent to the scene.
Crews treated five patients, one in a moderate condition and four in a minor condition.