St John is rolling out a new fleet of ambulances to prevent paramedics from getting injured when helping heavy patients.
The ambulance service is investing $8.6 million in 43 new vehicles.
St John's head of clinical support, Murray Holt, said the new design was the result of feedback from ambulance officers.
The new ambulances had "game changer" electric stretchers.
They meant staff did not lift the patient into the back of the ambulance - "the stretcher lifts itself".
He said the new design would mean fewer back injuries for paramedics.
About 10 were injured each month lifting or handling patients.
"We are, over time, seeing a higher number of very heavy patients.
"The new stretcher has the capability of lifting up to 318kg, so that provides the capability for us right across the country to deal with those very heavy patients."
In the past six years, the number of obese patients transported by the ambulance service more than doubled.
Auckland ambulance officer Mat Delaney said, despite best practice, it was easy for staff to be injured.
"We do a lot of lifting, and often they're awkward lifts or heavy lifts.
"We try to mitigate those risks as much as possible, with education, with exercise, stretching and technique, but at the end of the day, 300kg, that's a lot of weight to be lifting."
The new ambulance design also made it easier for staff to wear seatbelts while treating patients.
Ambulance Association chairman Mark Quin said heavy lifting was the leading cause of back injury among ambulance workers.
Ongoing problems from back injuries could lead to "hundreds of hours off work".
"Anything we can do to reduce that risk is good news."
Obesity expert Dr Robyn Toomath said the new design was "especially good for people who suffer from morbid obesity".
"The last thing they need when they're feeling sick or unwell is to feel anxious about injuring someone else or the possibility that they can't get to hospital because of weight problems."
The ambulances should be rolled out by November.