Some Auckland ambulance patients are being taken to Whāngarei Hospital because North Shore Hospital is too full to take them.

That is despite the much smaller Whāngarei Hospital already struggling with extremely high patient numbers this winter.

RNZ understands diversions were taking place on Tuesday night which was also very busy at Whāngarei's emergency department.

Diversions were happening also last week.

Tim Malloy is a GP for Coast to Coast healthcare group which has a clinic in Auckland's most northern town Wellsford, just shy of the Northland border.

He was sent a letter by St John Ambulance last week telling him any patients from the northern part of the Rodney district who needed to go to an ED would be taken to Whāngarei. They were normally serviced by North Shore.

That was "due to the huge demand on the services at North Shore Hospital", he said.

RNZ understands Whāngarei was already under serious pressure itself. It is about half the size of North Shore.

Health NZ director of operations Brad Healy said it was a "very small number" of ambulances who were actually diverted to Whangarei.

"This practice is not unusual and used at times to manage demand and ensure patients can receive care as quickly as possible. In some instances, depending on the location of the patient, Whangārei Hospital is closer in travel time than North Shore Hospital," he said.

Malloy said the letter was the first his practice had ever received about the ambulance diversions.

Busy winter in northern Auckland

This winter was the busiest Malloy had seen in 37 years as a GP.

Patients in Coast to Coast's urgent care clinic were sometimes waiting five hours and staff have had to be brought in on their days off to help, he said

"When you have 15 people waiting for you and you have a serious illness you are trying to manage in a patient while you wait for an ambulance to arrive, and all these patients are just having to wait, it's incredibly stressful. For all of us," he said.

Most of the patients coming into urgent care had respiratory infections. The cases seemed to last longer - and there were a growing number of secondary infections, he said.

There were very high numbers of people with influenza.

Malloy wanted to see a campaign to encourage people to get vaccinated against flu - and for those vaccinations to be free.

It would help people stay healthy, in particular to avoid serious complications.

That would help the whole health system, he said.

"The burden on our hospital EDs in particular is ridiculous and we need to be doing everything we possibly can do as a whole society and as health providers to prevent that from happening," he said