Five patients with influenza are in Christchurch Hospital's intensive care unit and another 80 in isolation wards, as pressure rises on an already fragile health system.
Hospital admissions for winter-related illnesses have surged dramatically over recent weeks and medical centres around the city are also reporting a sharp rise in the number of patients arriving with flu symptoms.
Canterbury District Health Board chief executive David Meates said people should contact their GP if they were unwell and be immunised against the flu to avoid getting sick.
"If you are feeling unwell, stay home and if your condition deteriorates phone your general practice team," he said.
Influenza strains likely to be circulating this winter include H3N2, a subtype that can infect birds and mammals, H1N1 that was the most common cause of flu in 2009 and Influenza B, a type that can infect any time of the year.
Symptoms for all strains include runny nose, sore throat, aching muscles, headache, cough, Nasal congestion, malaise, fever, watery eyes, aching joints, chills and fatigue.
Burnside Medical Centre practice manager Maree Mabey said her surgery was "flat tack".
"We're turning patients away and giving general advice over the phone because some people don't want to pay big money to go to the emergency clinic," she said.
Centre doctor Len Redoblado had come down with the flu himself and was now wearing a surgical mask when seeing patients.
"We've had a few irate patients not wanting to go to other (doctors) and our nurses are flat out as well," Ms Mabey said.
"There's no rest for the wicked, as they say."
Harwood Medical Centre practice manager Johanna Geertsema said the centre's three doctors had been busy for the last few weeks treating flu symptoms and it was difficult for patients to get an appointment.
"But if it's an emergency, we'll always see people," she said.
"A lot of people are phoning in with flu symptoms and we're just recommending bed rest and that they stay at home."
Ms Geertsema said people moving in with family members following the earthquakes and living closer together allowed the flu to spread more quickly. Dr Stuart Kennedy, of the Hornby Medical Centre, said he'd noticed an increase in flu symptoms in the last few weeks but was managing the situation.
"We've had an awful lot of sore throats and sniffles, rather than full flu viruses," he said.
Dr Kennedy said he advised people with flu to stay at home rather than visit the surgery.
"We've got masks if people think they have a nasty one," he said. "We only see the ones who are really crook coming in."
Canterbury Employers Chamber of Commerce chief executive Peter Townsend said there was "plenty of flu about" but employers were reporting "just the normal absenteeism".
"It's not as bad as it could be, considering this was always going to be the winter from hell after the earthquakes," he said.
Mr Townsend said the "big issue" was whether the health system could cope.
"Employers need to take a particular interest in the health of their employees this winter because resources are pretty stretched."