The closure of State Highway 6 between Fox and Franz Josef Glaciers on Saturday meant a woman with a heart condition could not be reached by ambulance.
Police say St John contacted them at about 3am on Saturday because they were unable to get to Fox by road or by air.
The Whataroa policeman was woken a couple of hours later to drive ambulance personnel to Fox in a four wheel drive vehicle.
A slow trip was then made back to Franz Josef where an ambulance took her to Greymouth Hospital.
Police say the weather also stopped several cars and a bus from getting beyond Fox Glacier.