New Zealand is experiencing increased rates of influenza this season, experts say.
A National Influenza Specialist Group (NISG) spokeswoman said both influenza A and B viruses appear to be spreading widely, with the A virus being dominant in the North Island and the B virus dominant in the South Island.
She said recorded rates of influenza have nearly reached last year's peak, despite flu season not ending for another two months.
"This virus distribution pattern may change as the season progresses," said virus expert and NISG spokesperson, Dr Lance Jennings.
Health professionals have also said the patterns of the influenza viruses (A and B) have not been seen like this in New Zealand for 30 years.
Data from the latest Environmental and Science report shows 140 cases of the influenza A strain in the North Island this season alone, compared with just three in the South Island.
The South Island has reported 34 cases of the B strain, compared with 32 in the North Island.
Environmental Science and Research communications manager Stephen Corbett said the A strain was clearly predominant this season.
He said this year so far there were 405 reported cases of the A strain in the North Island and 41 in the South Island.
The report also showed a total of 136 consultations for influenza-like illness were reported from 61 general practices in 18 out of 20 District Health Boards between June 29 - July 5.
This shows a weekly consultation rate of 42.1 per 100,000 patients.
The A virus is usually more serious while the B strain tends to produce severe infections but has lower death rates.
Both strains can be fatal and experts warn those at risk to seek help at the first symptoms.
People over 65, those who are pregnant and those with respiratory conditions - in particular people aged over 65 and under five are most at risk by the flu.
The virus is contagious for 10 days after symptoms appear in children and between three and five days for adults.
As of the end of last month, only 26 percent of the population had received a flu vaccination.
Officials are now extending the free flu immunisation programme by another month.
Health Minister Jonathan Coleman says the programme is being extended from July 31 to the end of August to help ensure people have the protection they need.
"The A-H3N2 strain, which is covered by the vaccine, appears to be the predominant type - this strain affects the elderly and very young more severely than other strains," he said.
The flu jab is free for people over 65, pregnant women, people with long term health conditions like severe asthma and children under five who have been hospitalised for a respiratory illness.
People with Down Syndrome and those with cochlear implants are also eligible for the free vaccine.
Those not covered by the free programme can still get vaccinated, though there is a fee involved.
To date almost 1.2 million flu vaccines have been distributed across the country, Dr Coleman said.