Free flu vaccines for children aged under five are now available, as the health system struggles with the worst outbreak in years.

Associate Minister of Health David Seymour was in Auckland with Minister of Health Simeon Brown where they announced the changes to flu vaccine funding criteria.

Pharmac's extension of free flu jabs for children between six months and five years of age begins on Tuesday - rather than from 2027 as announced last week.

The ministers said the decision was in response to patients asking for vaccines sooner, with more than 260,000 young children now eligible.

Health Minister Simeon Brown (left) and Associate Health Minister David Seymour. Photo: RNZ

"Young children get sicker from the flu than most people realise, and they are more likely to end up in hospital, with the youngest infants at the highest risk of all," Brown said.

Children under five years old have had the highest rates of hospitalisations during this year's flu outbreak - one of the most severe in years.

"Flu season puts a lot of pressure on households, workplaces, schools, and the health system. Today's decision will give families the support they need to manage the flu this year," Seymour said.

Emergency departments had seen record numbers of people and struggled to cope with staff off sick.