Three firefighters are being treated in hospital after responding to a workplace incident where two people were found unconscious inside a solvent hopper.

Two seriously injured people were also rushed to North Shore Hospital after being exposed to an unnamed chemical inside the hopper - an industrial device for loose, bulk material which can open at the bottom.

Police and St John Ambulance also responded to the workplace accident in Wairau Valley, on Auckland’s North Shore. WorkSafe was making inquiries.

Fire and Emergency NZ Tāmaki Makaurau on-call Commander Brad Mosby told the Herald they were “wrapping support around our firefighters in hospital”.

Two crews responded to a report of a medical event shortly after 11.30am.

“On arrival, they came across two patients unconscious inside a solvent hopper,” Mosby said.

Firefighters rescued the two people, who were both in a serious condition, he said. He said they had been exposed to an “unnamed chemical”.

“[It was] an incredible effort by firefighters on scene to perform these rescues,” Mosby said.

 “As a result,” Mosby said, “our firefighters have been admitted to hospital as well for observation on the advice of St John.”

He said the crews were wearing breathing apparatus but they had been admitted to hospital as a precaution while they tried to work out what the “unnamed chemical” was.

A spokesperson for St John said the two people were taken to North Shore Hospital after they got a call to Hillside Rd at 11.33am. Two ambulances and two support vehicles responded.

A spokesperson for police said WorkSafe was the lead response agency but police remained at the scene.

A WorkSafe spokesman said they had been notified and were making initial inquiries: “Note, this is not an investigation at this stage.”