An outbreak of influenza is reaching epidemic levels, officials say.
The number of people falling ill in Canterbury is of particular concern with health services saying they are feeling the strain.
"GPs have become sick, some senior medical officers have also succumbed to influenza over the last week or two, so as well as extra patients there's less staff," Canterbury Medical Officer Alistair Humphrey said.
Fifty patients are staying in an isolated ward at Christchurch Hospital with influenza, while another five are being treated in intensive care.
The city's 24-hour surgery has also been inundated with admissions recently with around 300 patients on a weekend.
Humphrey said the influx of patients has had a knock-on effect in other areas.
"There have had to be a few, a few not many, but a few elective procedures cancelled because of lack of availability of ICU beds."
The city's overcrowded and cold housing conditions are being blamed by some for the spread of the illness, and Humphrey said these issues do need to be addressed.
While the Auckland region currently has the highest number of flu cases in the country it is a different strain to the one affecting Cantabrians.
The South Island's H3N2 strain is more serious and hospitalises more people. Its symptoms include hallucinations and crippling nausea.
Officials say the strain is expected to be as severe as the H1N1 swine flu which killed 49 people in 2009.
The Canterbury Health Board said it is not too late to get vaccinated.
- with Newstalk ZB