St John Ambulance has had to close its main ambulance building in Christchurch because of earthquake damage.
It is running twice the normal number of ambulances to ensure a smooth service.
The earthquake and its aftershocks have posed big challenges for the region's ambulance provider.
Red notices decreeing the main ambulance station and a command building unsafe have forced St John to cram all its staff into a newer wing.
St John's operations manager, Chris Haines, says because of the stress and the lack of people out in the CBD, most jobs at the moment are medical problems, rather than the normal accidents from excessive drinking or sporting activity.
Extra resources from outside the region are helping run 13 ambulances around the city rather than the normal six, after 10 specialist paramedics and 38 welfare staff answered a call for help last week.
Mr Haines says the volunteers have been invaluable, but will have to be let go soon.
He says they expect to be back to normal numbers within the next week.
Like all the other emergency services, St John is shifting its focus from emergency response to the recovery phase.
It says it was already planning to overhaul its main ambulance station and the earthquake has just made the project more urgent.
