WHO Director-General Dr Tedros Adhanom Ghebreyesu has warned of a "rapid escalation" in cases, with more now reported outside of China, where the illness originated, than inside.

As of Monday, the Ministry of Health said 514 negative tests had been conducted in New Zealand, with eight confirmed cases and two probable cases.

The Prime Minister said her message to clinicians is that if they need to test then they should do it, because she says the capacity is there.

"We have the capacity, we are continuing to build capacity, and now it's up to those health professionals on the ground to make those decisions and test," Ardern told reporters.

"Ultimately, I'm not the doctor in the room making those decisions, but the message I will send to clinicians is we have the capacity; we have the ability to test far more than we are now and my message to them is if in your judgment you need to, then do."

Health Minister David Clark said he's aware of "a lot of man work going on" across the health system to "make sure that if it is put under pressure the health system is able to cope".

Dr Clark said there is currently 239 intensive care units (ICUs) across the country and 263 negative pressure rooms, an isolation technique used in hospitals and medical centres to prevent cross-contaminations.

He said there are "varying levels" of ventilators in New Zealand, machines designed to help with breathing - important in the fight against COVID-19 which is known to cause difficulty breathing in some patients.

Dr Clark said the Ministry of Health is looking at "how best to deploy" the machines if New Zealand ends up with an outbreak of the coronavirus.

"At the moment, all of our effort is going into making sure that we don't have too much burden on our health system because the best approach is prevention."

Testing for COVID-19 is free in New Zealand and more information can be found here.