The service, which can be called to any incident across Southland, is looking to fundraise for a new station.
Nationally, St John has started a campaign to construct 14 stations across the country with Invercargill being one of those.
The government funding St John receives does not include the upgrading or replacing of ambulance stations.
St John Southland area operations manager Braden Stark said St John in Invercargill was bursting at the seams and there was nowhere to grow.
The operations are based in Jed St while the administration office is in Tay St and training is done out of a building in Victoria Ave.
"It is not ideal. The biggest issue we have is we have expanded over the years and now there is just no room.
"That is why we have ended up in three different sites", he said.
The ambulances were situated alongside the Fire and Emergency NZ appliances but there was no more room to move into, he said.
The service employs about 40 people fulltime in Invercargill.
Demand for emergency services in New Zealand has steadily increased over the past 10 years due to an increasing and ageing population, and the additional pressures of extreme weather and health events.
Southland was no expectation and the station was the Southland hub, Mr Stark said.
With increased demand brings more pressure on staff and facilities and though they were coping, they could not go on having operations in three different sites in the city, he said.
Mr Stark said increased demand could be put down to a rising population and people getting older.
Limited GP service also did not help.
St John had bought land in Clyde St 18 months ago for a station, which would house all operations on the one site.
Mr Stark said the new site had ticked all the boxes in terms of closeness to the hospital and to other parts of the city.
"We were lucky as good space in the centre of the city is at a premium."
A ballpark figure for the development was set at $10 million though that may change.
He said operations were still working at the moment but the time was going to come when it would not be workable.
Mr Stark said Southlanders were known for supporting good causes and he hoped this would continue when raising funds for the new station.
The fundraising began with a giving day appeal which was part of the Light the Way appeal which took place on Friday, where every dollar donated was matched by St John’s major sponsors.
Over the next two to five years, St John needs to raise over $40m to complete the 14 station projects.
Oamaru is also one of the stations which has been listed as needing a rebuild.
