Covid 19 coronavirus Delta outbreak: Virus rife among returnees at Crowne Plaza Hotel

Travellers enduring managed isolation at the highly Covid-19 infectious Crown Plaza Hotel should be able to leave as expected this evening.

However, the family of three who tested positive on day 12 of their stay will have to remain at the hotel.

Director general of health Dr Ashley Bloomfield this afternoon revealed the cluster associated with Auckland's Delta Covid-19 outbreak has grown to 21.

That included the Air NZ staffer - a woman in her 60s - who tested positive after returning from a flight from Japan, and is still "unlikely" part of the Devonport man's community transmission.

Prime Minister Jacinda Ardern also added this afternoon that they had honed in on the likely source of the outbreak to a returnee from Sydney who came back on a red zone flight on August 7.

The person returned a positive test result on August 9 and was transferred from the Crowne Plaza to Jet Park that same day.

The person was then taken to Middlemore Hospital on August 16.

The current community cases most likely came from the traveller, Ardern said.

A family next to a case at the Crowne Plaza has now tested positive on their day 12 test.

Ardern said they could now expect a "high level of infectivity".

A hold had been put on some departures from the Crowne Plaza overnight, after the three people had tested positive.

They had been asked to stay longer as CCTV footage was examined and to wait for genome sequencing results, which were expected later today.

Returnees on other floors at the facility scheduled to leave today would be able to do so, Bloomfield said.

Middlemore Hospital was not a line of investigation at this stage.

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Of the 208 staff at Crowne Plaza who were there at the same time as the returnee, only one was now overdue for testing and by less than 48 hours.

Of 200 staff working at Jet Park, only two are overdue for testing.

Vaccination compliance had been high across both sites, Ardern said.

Ardern added that of the 12 of the 21 confirmed in the Auckland cluster, a further eight were being investigated.

Two community cases were taken to North Shore Hospital overnight.

One had "worsening symptoms" and the other had underlying conditions. Both were in a stable condition.

Bloomfield said 362 close contacts have been identified but by the end of today there would be "well over 1000".