Influenza and respiratory viruses are behind the largest spike in callouts by Wellington Free Ambulance for any August in eight years.
Spokesperson Rob Ives said they took almost 5,000 calls last month.
"It's been particularly busy because of the severity of the flu symptoms we've been seeing around the region."
Mr Ives said extra staff were put on to cope with the increase, but patients were not at risk from any delays in their response time.
He said the elderly, children, diabetics and people with respiratory disorders had been hardest hit.
He said there was an expectation that callouts for paramedics would drop down over September and October, as weather conditions improve.
In the future, Wellington's workload is expected to increase, but only marginally. "We've had an operational demand analysis done last year by an external company," said Mr Ives.
"They've predicted our workload over the next five years through to 2018 and we expect a 1.4 percent increase on a yearly basis."
The Institute of Environmental Science and Research say about 1,600 cases of influenza-like illnesses were reported to doctors across New Zealand during August.