Officials have shed more light on the mysterious Covid-19 infection at Auckland's St Lukes shopping mall - including a possible link to a bus ride.

It was revealed today that an infected Westfield St Lukes worker may have been on the same bus as another positive case on August 12, which underlined the importance of wearing a mask on public transport.

Earlier, the case - an employee who worked at the mall for a number of days while infectious with Covid-19 - was put "under investigation" after initially being connected to the cluster.

But today, director general of health Dr Ashley Bloomfield said there was new evidence through ESR genomic sequencing to put the two back together.

An infected Westfield St Lukes worker may have been on the same bus as another positive case on August 12. Photo: NZ Herald

But there was as yet no known or confirmed epidemiological link to the outbreak, he said, and inquiries continued into the source of exposure.

"One specific line of inquiry is that this case and another case may have been on the same bus, and I'd like to take the opportunity to remind everybody of the value and importance of using masks in places, particularly like public transport."

Authorities were now working with Auckland Transport to locate others who may have been on the same bus - something that was being aided through HOP card data.

Bloomfield couldn't yet say where the bus was headed.

There are now eight people receiving hospital-level care for Covid-19 - two in Auckland City Hospital, one in North Shore and five in Middlemore.

One person at Middlemore remains in ICU.

One person in Waikato was hospitalised but not related to Covid-19.

There are 143 people linked to the cluster who have been moved into the Auckland quarantine facility. This includes 70 people who have tested positive.

There are now 1315 confirmed cases, and 105 active cases.

The two imported cases have been transferred to the Jet Park Hotel.

There were 15,714 tests conducted yesterday.