Emergency services were called to Cove Rd in Waipu about 7.50pm yesterday.
The St John ambulance had two officers on board, transporting a patient in a moderate condition from Mangawhai Heads to Whangārei Hospital.
One ambulance officer was treated for moderate injuries and taken to Whangārei Hospital, along with a person in a critical condition.
The other officer and the patient on the ambulance were not injured in the crash, and the patient was transported to hospital by another ambulance.
The damaged ambulance has been taken off the road for repairs, a St John statement said.
"Hato Hone St John takes the health and safety of the public and our people very seriously.
"We will assist police with their investigation. Support will be provided to our ambulance staff involved; our thoughts are with everyone affected by the incident."
