Ministry of Health director-general of health Dr Ashley Bloomfield has confirmed the latest coronavirus case, the fourth in New Zealand, attended a Tool concert at Auckland's Spark Arena on Friday night.

A man who tested positive for coronavirus attended the Tool concert at Spark Arena in Auckland last Friday when he may have been infectious, the Ministry of Health says.

Earlier, the ministry confirmed the person was the fourth to test positive for the illness - he was the partner of the second person to test positive for the virus.

"We encourage all people who were in the general admission standing area to be aware of the general symptoms of Covid-19," Ministry of Health director-general of health Dr Ashley Bloomfield said. If people are symptomatic, they were asked to call Healthline's dedicated coronavirus number - 0800 358 5453.

The man was standing in the left quadrant.

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"Those people who were in the standing area were casual contacts, they are not close contacts," he said.

DUNCAN BARNES There was no way to know who was nearby the confirmed Covid-19 case at the Tool concert, Bloomfield said.

There could be a hundred casual contacts with the confirmed case who attended the Tool concert. These people were of a very low risk.

Spark Arena said they would not be commenting on the issue and referred all queries to the Ministry of Health.

Bloomfield said there was general advice to all people considering attending large gatherings: "If people are not well, then they shouldn't be turning up."

Close proximity was defined as within a metre of the infected person for more than 15 minutes.

There was no way to know who was nearby the confirmed Covid-19 case at the Tool concert, Bloomfield said.

Close contacts of the second person to test positive were already in self-isolation, and the man had been in self-isolation since Wednesday, he said.

Ross Giblin/Stuff Ministry of Health's Director-General of Health Dr Ashley Bloomfield. Earlier the ministry confirmed a fourth positive test for coronavirus in New Zealand.

"He does not require hospital level care".

FATHER, FAMILY OF THIRD POSITIVE CASE TESTED

The father of the third person to test positive, who is thought to have transmitted the disease from Iran, was still being tested.

If a positive test result was returned, he would be considered a confirmed case, Bloomfield said.

Symptomatic family members would be tested, and those without symptoms would be offered testing, he said.

NZ Steel had warned its workers they may have been in contact with a case. Close contacts had been advised.

There was no risk to schools named in recent days, he said.

As to people who might have been travelling on the same flights, it was virtually impossible to identify who might have been nearby the Covid-19 case - such as sitting next to to the second person to test positive - at an airport gate as they travelled from Auckland to Palmerston North, Bloomfield said.

Such people were considered casual contacts, not close contacts that would require self-isolation.

Restrictions would remain for people travelling from China and Iran, those travelling from Northern Italy will be met by a "strengthened" health team at airports, Bloomfield said.

Meanwhile a group of mountainbikers from Italy travelling through New Zealand were now in self-isolation, he said.

HUNDREDS OF TESTS

Overall, there have been 217 negative tests and four positive tests in the country.

The results of each test took a day to come through, and were generally received in the evening. The person must then be notified of the result, and a thorough interview was then conducted to trace the person's movements.

"We want to find cases. Finding cases indicates success, not failure. It's fundamental for our effective public health response," he said.

Healthline had another "very big day" on Thursday, Bloomfield said.

He repeated the advice to wash your hands for 20 seconds, and to cough into arms rather than hands.

NEW STRAINS: REPORTS

There had been initial reports of other Covid-19 strains in China, but it was very early information and more investigation was required, Bloomfield said.

Meanwhile Bloomfield said New Zealand had a large reserve of masks.

"We have got our own mask-producing factory here in New Zealand," he said.