A public health expert says the time is nearing to loosen testing standards for coronavirus, so people who are symptomatic without having travelled can be tested.

On Thursday, the Ministry of Health confirmed New Zealand's first case of the virus being transmitted within the country, the third confirmed case overall.

AP Testing for the virus could be expanded, a public health expert says.

The man, in his 40s, had family members travel to Iran, and it is likely one of his relatives had a mild case of the virus.

Ministry of Health testing guidelines currently recommend testing only if the person is both displaying symptoms and has travelled to a high-risk country, or have been in close contact with a Covid-19 patient.

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On Tuesday Stuff reported a senior doctor at Wellington Hospital was concerned about tests being denied for people showing coronavirus symptoms.

Otago University 's Head of Preventive and Social Medicine, Dr Patricia Priest, said she believed the time was nearing to loosen the criteria.

"Testing people with pneumonia, for example."

New Zealand did not want to be in a situation where Covid-19 went undetected while being transmitted in the community.

"It's all difficult judgement calls about when you start looking in the community, even though you think it is probably not actually there yet."

She said there were limited resources available, and there was a balancing act to taking a broader approach.

GETTY IMAGES Three cases of coronavirus have been confirmed in New Zealand.

New Zealand's third case showed how difficult it could be to contain a virus when people showed only a few symptoms.

The case illustrated the kind of information the ministry needed to take into consideration when looking at testing standards, she said.

On Thursday, director-general of health Dr Ashley Bloomfield said there was currently capacity to do 550 tests a day.

"Additional capability of up to a further 1000 daily tests will be coming onstream over the next couple of weeks."

The testing guidelines would not be updated at this time, a ministry spokesperson confirmed.

DEAN CARRUTHERS/STUFF Dr Siouxsie Wiles, a microbiologist at the University of Auckland.

Microbiologist at Auckland University, Dr Siouxsie​ Wiles, said New Zealand was not an outlier by having a travel aspect to testing standards.

They would likely be dropped as more countries saw larger outbreaks, or when the virus began to spread within New Zealand.

If a person was displaying symptoms but has been declined testing, her advice was to practice self-isolation.

If symptoms worsened, call Healthline on 0800 358 5453.