Last year the service cared for 425,000 patients and its 696 ambulances and other operational vehicles travelled a combined 19.3 million kilometres.
The new models cost about $200,000 each to buy and equip.
"They have more space inside, are better configured and have modern defibrillators and other high-tech medical equipment," Holt said.
Basic chassis are imported from Mercedes-Benz in Germany in batches of three and it takes about two months to fully equip them at workshops in Hamilton.
The ambulances will be deployed in equal numbers between the Northern and Central regions and the South Island.
St John replaces about 35 ambulances a year out of a national fleet of 700. A front line ambulance's life span is approximately eight years or 440,000km.
"We expect to need more vehicles on the road in the next two years than we have at present," added Holt, "and ongoing fundraising efforts from the public are never taken for granted."