Flu-related hospitalisations in Auckland have doubled in the space of a week, as the country's flu season begins to bite slightly later than usual.

Dr Hannah Cooper, a public health physician in the health intelligence team at PHF Science, said in recent weeks - particularly the past seven days - cases have climbed sharply.

"In the past week [there's been] an increase in flu-related hospitalisations in the Auckland region. They actually doubled in the previous week compared to the week prior."

However, they were still within the normal range for peak season seen in previous years.

For the week ending 9 August, the rate was 3.781 per 100,000 people - up from 1.574 the week before.

"Flu, particularly in cold weather, spreads more easily," Cooper said.

The cold snap had seen more people spending their time indoors, spreading the virus more effectively.

Last year's season was late too, which had pushed the 2026 season later in the year, with people retaining some immunity from last year's infections.

Public awareness of the different strains was also on the rise.

"Now that you can do a test from the pharmacy to see what kind of cold or flu virus you have… that's really raising awareness about flu activity," said Cooper.

Despite the spike in cases, the vaccine was proving effective, according to their data.

"The really good news is that the flu viruses that are circulating this season are a very good match. The vaccine is a very good match for those viruses."

It wasn't too late to get the vaccine, she said.

Emergency departments (EDs) and services around the country are also feeling the strain.

St John declared a "major incident" last week, after a "highly unusual" sudden spike in demand correlated with the recent cold snap, and an influx in people requesting ambulances for winter illnesses such as influenza and respiratory issues.

EDs remained over capacity in many areas - Wellington had its busiest day in more than a year earlier this week.

Nurses Organisation delegate Ryan O'Connell, who works in the Wellington ED, said: "For about three or four days in a row, we were getting over 200 patients per 24-hour period. Anything over 200 is usually quite high for the ED."

It was "harsh on morale", he said. "You've just got this waiting room filling up with people you triaged hours ago and wish were at least lying down on a trolley at this point."

"There's so many people to look after and not enough staff and not enough room to look after these people. But you make do anyway and you try your best."

Pressure on GPs was meaning appointments were scarce, which left people turning to EDs when their condition worsened.

"I constantly see patients and triage patients who say, 'I was trying to get a GP appointment… maybe I couldn't get one this week, and I'm just not coping with this at home.'"

With the main centres slammed, he felt for those in the more rural parts of the country.

"If a tertiary hospital in Wellington is suffering from this overcapacity and understaffing, then I can only imagine what it's like for the smaller centres who don't have as many resources."