A nasty winter flu strain that is doing rounds is leaving hospitals in some parts of the country struggling to find bed space.
Over the past two weeks, the number of those coming to Christchurch Hospital with influenza-like illnesses has trebled.
"We've got 17 patients in the hospital at the moment with influenza, but five of those are in the Intensive Care Unit, and they're still coming in," said Canterbury Medical Officer of Health Dr Alistair Humphreys.
Middlemore Hospital is also bursting at the seams.
"We have had days this week of over 104% occupancy, which is making things really busy for us," said Dr Vanessa Thorntons from Middlemore Hospital.
Lab staff have found the main strain in Canterbury is influenza A. It is not a new strain, but has not been seen much over the past six years, and can be more severe than other strains.
"Overall there was very little influenza activity last year. So this is one of reasons why population level immunity is probably low at the present time and we're seeing increased activity," said virologist Lance Jennings.
"What happens with influenza is they start off explosively in one or two centres, and in subsequent weeks it spreads throughout the country."
While it was included in this year's flu vaccine, young adults have been slower to get immunised and the virus is mainly hitting those aged between 20 to 40.
So far the outbreak is mainly around Canterbury and Auckland where rates are higher than normal, but less severe strains are sprouting up elsewhere and experts fear it is just the start.
Thorntons said that is a concern, especially as schools head back after the holidays.
"If we're this high now, it actually means we're going to be working even harder in the next couple of months," she said.