Covid-19 Response Minister Chris Hipkins' comments come as the Government awaits results of genome sequencing from Australian health officials.
Hipkins had been assured as soon as Australian authorities had the results, they would share it immediately.
He expected this to occur this evening but already they were assuming it was the Delta variant.
"We are working on the basis it is likely to be the Delta variant. The advice from Australia is that it is linked to their outbreak [in Sydney] at the moment, which is the Delta variant.
"From past experience the time to do genome sequencing can vary, depends on the strength sample."
Earlier today, Hipkins said there were no new cases of Covid-19 in the community or in MIQ to report.
However, he cautioned "it's still early days".
There were around 7000 tests processed, more than 1200 in Wellington region - four times more than usual.
Hipkins said the Government is still waiting for the genomic sequencing results from Australia after the Sydney man travelled to Wellington at the weekend while infected.
The man's partner, with whom he travelled, is asymptomatic and tested negative for the virus.
The traveller had one vaccine dose about 10 days ago. His partner had one dose also.
There were 420 contacts attached to the contact tracing database who were in locations of interest at the same time as the Sydney man, including 58 who were on the flight to New Zealand. All those on the flight were close contacts.
People were being asked to isolate for 14 days for a reason, regardless of if they returned a negative day five test, Hipkins said.
