Health Minister Tony Ryall says the Government is extending the period for free flu vaccinations for eligible groups by a month.
He says it will now run until 31 August instead of finishing at the end of this month.
The Institute of Environmental Science & Research says the rate at which people visited their doctor with flu-like illnesses doubled earlier this month, with the highest rates in Waitemata, Counties Manukau and Canterbury.
Mr Ryall says the numbers are still normal, because last year was a particularly quiet year for flu, and hospitals have plans to deal with the pressure.
Fewer flu jabs have been given so far this year and Mr Ryall says there are about 20,000 doses in stock within the current budget.
Those eligible for it are pregnant women, people over 65, those with chronic health conditions and Canterbury residents between six months and 18 years of age.
