Ambulances were called to 1373 incidents a day across the country last week - the busiest in St John's history.
St John clinical operations director Norma Lane said the organisation was coping with the extra work.
"Our St John Clinical Control Centres are constantly monitoring our resources and managing our capability through the busiest time of year, with extra resourcing placed where the need is greatest."
She asked people to be prepared to help prevent the need for ambulance callouts.
"Please dress warmly, drive to the conditions, make welfare checks on elderly neighbours and make sure your regular prescriptions are filled."
July and August were usually the months with the largest workload for St John, so ambulances were likely to be called out even more.
More callouts were for flu-like symptoms and respiratory problems than any other type of illness or accident over winter.
Winter sports injuries also contributed to the additional numbers, St John said.
In some regions, ambulance crews' workloads increased even more than Hawke's Bay.
Calls from the Auckland region were up 12 per cent on June last year and in Waikato 8 per cent more ambulances were called out.
The number of incidents St John attends is always about 10 per cent higher in winter months than the rest of the year.
St John advised people to visit their GP for non-urgent health problems or call Healthline for advice from a nurse, and continue to call 111 in an emergency.