St John Ambulance admits it has had cases where callers have been told an ambulance is on its way when in fact it is not, but said that had never resulted in a catastrophic outcome.
The ambulance service is a month into trialling a new system in Auckland where if a call is designated as low priority by the emergency call taker, a paramedic or nurse calls back to give a fuller clinical assessment.
It experienced a 10 percent increase in non-urgent cases and a 3 percent increase in demand for services overall.
Clinical director Norma Lane told Radio New Zealand's Nine to Noon programme some people who had complained had been frustrated at being asked a list of questions, but that was necessary to determine the right outcome.
"What we want to do is to support people who have a problem that actually could be resolved other than sending an ambulance."