To that end, St John has been working toward establishing a second base on the eastern side of the city to speed up response times.
Wanganui territory manager John Stretton said: "For the size of its population, Wanganui is very spread out. Our ambulance base is on the western side but we have a lot of people living on the eastern side.
"Having a second depot, preferably somewhere like Wicksteed St, would improve our response times to places like Wanganui East and Aramoho."
Mr Stretton said the service aimed to arrive at an emergency in the urban area within eight minutes at least 50 per cent of the time.
"We have very clear guidelines about the speeds we can drive so sometimes that eight minutes is stretched."
Another ambulance base would make that target easier to reach.
In response to an increasing workload and to cover burgeoning costs, St John is increasing its callout fee.
Nationally, St John received 380,785 emergency calls in the year to June - 14,276 more than the previous year - and as of April 1, patient charges will rise to a single rate of $88. Wanganui residents have previously been paying $75.
The flat rate charge for those not covered by public health services will also jump from $769 to $800.
The charges cover patients who need an ambulance because of a medical emergency. People who have suffered an accident don't pay anything as long as the callout is within the first 24 hours of the injury and meets ACC criteria.
St John operations director Michael Brooke said the increased demand could be attributed to a number of reasons, ranging from a growing population to an ageing population with more chronic health needs.
Funding had recently been approved for 57 new paid staff around the country at a cost of $4 million, he said.
St John has 1043 paid staff and 2951 volunteers who treat more than 415,000 people every year.