At least 12 more volunteers were needed, residents were told at a public meeting in Owaka on Wednesday night.
St John Waitaki area rural support officer Ken Barton said eight volunteers were each working about three shifts a week to keep the service running.
''We really need to know if you still want your ambulance service. We have a small group who are working really hard. We need your support.''
A volunteer crew of 20 would be enough to keep the service viable, and any more would be a bonus, he said.
Owaka St John team leader Karen Bradfield said for the past few years volunteer numbers were so low only night shifts were covered.
''We're committed to this job and the community. We do what we can, but we would like to do more.''
The Owaka station covers halfway to Balclutha and through the Catlins. It is covered by Balclutha during the day.
There had been 119 incidents over the past 12 months, with 26% of these (31) responded to by Owaka and 56% (67) by Balclutha.
''It's not a busy caseload. You don't have to panic that you will be worked off your feet,'' Mrs Bradfield said.
The Owaka area committee was willing to fund some accommodation in the township for those who lived out of pager coverage, in order to have enough volunteers.
Shifts were flexible, and most volunteers would work about three shifts a month.
Mrs Bradfield (57) has been a volunteer for 23 years and said having an ambulance service based in the township cut down waiting times, and offered some ''peace of mind'' for residents.
The Owaka team was very passionate about St John and worked hard to provide cover for the area.
Over the past two years, St John staff in the Waitaki area - which covers from Geraldine to Owaka - have attended 36,274 callouts. Most of these are classified as ''emergency ambulance service'' or urgent work, with only 4180 patient-transfer jobs.
Mr Barton said the shortage of volunteers was not limited to his area, but was a national issue.
As a charitable organisation providing vital services, volunteers are the lifeblood of St John.
Just 1700 of the 10,000 adult New Zealanders involved with St John are paid for their time.
