Hospitals are being stretched to breaking point by the worsening coronavirus outbreak and will need extra support, union bosses say.

The Ministry of Health confirmed New Zealand's fifth case of the virus on Saturday.

It is treating two others as probable cases - one, a woman who returned to New Zealand from the infected Grand Princess cruise ship docked off California; the other, a family member of two of the already-confirmed cases.

Director-General of Health Ashley Bloomfield said hundreds of close contacts of the five confirmed cases had been identified, all of whom are in self-isolation for 14 days, including 43 staff from North Shore Hospital.

Dr Deborah Powell, national secretary for the New Zealand Resident Doctors Association, said medical staff were under extraordinary pressure, and District Health Boards had to prioritise their wellbeing.

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"We are stretched. We are really stretched," said Powell.

"It's not just our doctors and nurses, it's our laboratory staff and our radiologists."

"There are a whole lot of people in the hospital system that are stretched. There isn't any more give in our system anymore, we are at our limit."

PATRICK NGUGI/AP Hospitals around the world, like this one in Kenya, are struggling to cope with coronavirus.

Powell said DHBs needed to be treating clinical frontline staff "properly", including making sure they were adequately protected at work.

"They'll work themselves to exhaustion. They'll give it their all for their patients, really put themselves at risk because they care.

"They are carers. They work long hours, they suffer burnout, they're a dedicated, truly committed bunch of people."

As such, DHBs needed to make care of staff a "priority". "You've got to look after them. They will look after the patients."

NZRDA/SUPPLIED Dr Deborah Powell, national secretary for the New Zealand Resident Doctor's Association, says the pressure of coronavirus may be the straw that breaks the camel's back.

Powell feared the "double whammy" of a rapid increase in coronavirus cases coinciding with the flu season.

"People are turning up to ED with a cold and asking to be tested despite not meeting the criteria... [is an] additional load on frontline staff, to have to deal with people who are genuinely worried, but have no need to be."

She reiterated advice that people should phone ahead in the first instance of being symptomatic, and stay home. "The best way to contain this virus is exactly that, containment."

New Zealand Nurses' Organisation associate professional services manager Hilary Graham-Smith said coronavirus was going to place an "enormous strain" on the public health system. "Our hospitals and our resources are already really stretched."

ROSA WOODS/STUFF An isolation room at Wellington Regional Hospital which patients have to go through before entering a negative pressure room, which can be used to contain coronavirus. Director-general of health Ashley Bloomfield said on Saturday hospitals could dedicate entire wards to coronavirus.

Concerns had been raised about workers not having the right personal protective equipment (PPE) to keep themselves safe from the virus, Graham-Smith said, which had been brought up with several DHBs already.

Existing health and safety legislation outlines that workers must be appropriately protected.

Anxious members had approached Graham-Smith directly, asking whether the public health system would "actually be ready" to cope with a sustained community outbreak.

Many workers also questioned their employers directly about the country's state of readiness, she said.

"Where will those extra staff come from? That's the 64 million dollar question. We are already understaffed."

MONIQUE FORD/STUFF The Ministry of Health's director-general of health Dr Ashley Bloomfield remains confident in New Zealand's ability to manage an oubreak of coronavirus.

In disasters like the Christchurch earthquakes and mosque shootings, nurses and doctors typically "get their boots on and provide whatever is required", she said.

But the truth is, it's not known exactly how many people will be needed - it won't be known until the situation evolves, she said.

"Underfunding of the system is like a chronic condition in New Zealand. We see that in terms of the nursing workforce and pressure they're under on a daily basis. If we get a rapid increase in cases ... that would be significant cause for concern."

Director-general of health Dr Ashley Bloomfield said on Saturday that every DHB had been contacted to ensure they had enough PPE for staffers.

Healthline had been training "lots" of new staff to keep up with the increase in call volume.

There was a "whole range of things under way" to help the wider health system cope with an outbreak, Bloomfield said.

The health ministry had spoken with both the Medical Council and Nursing Council about re-issuing recently-retired doctors and nurses with practicing certificates, if extra staff were required.

Every DHB also had a "good plan" in place, which they were refining, he said. Hospitals could possibly look at shutting down entire wards to treat coronavirus patients, Bloomfield said.

Several DHBs contacted by Stuff reiterated they were "well placed" to deal with a coronavirus outbreak, however little detail was provided about what that would look like in reality.

Worldwide, there have been more than 101,000 confirmed cases of coronavirus, and more than 3400 deaths. New Zealand's health ministry remains adamant the risk of a sustained community outbreak is low.

In Australia, a doctor who has tested positive for coronavirus consulted about 70 Melbourne patients for five days while infected.

Health Minister David Clark was unavailable for comment.

Additional reporting: Hannah Martin