One person has been taken to hospital after a fire at a Fonterra factory north of Whangarei.

Multiple people were treated at the scene and all staff were evacuated from the plant at State Highway 1 in Kauri.

Emergency services were called at 7.30pm.

Initial reports suggested it was a chemical spill but Fonterra later said it was a small electrical fire.

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Fire and Emergency New Zealand (Fenz) shift manager Craig Dally said the fire had been caused by an electric motor that gave off fumes.

The smell of the fumes prompted concerns of it was a chemical leak, he said.

Several people had been treated by ambulance, Dally said, but he did not know the condition they were in.

"There was a small fire which had been extinguished by the time we got there," Dally said.

A Fonterra spokeswoman said it was just a small fire and there were about five people treated as a precaution.

"One person was taken to hospital for more precautionary tests."

Seven FENZ crews were at the scene, along with police and St John ambulance.