Genome sequencing of Covid-19 cases in managed isolation has revealed more people in managed isolation with the new very infectious variants.
ESR testing and whole genome sequencing has identified 11 cases of the UK strain and six cases of the South African in quarantine since 6 January.
The Ministry of Health said there are now a total of 29 samples of the UK variant and seven of the South African variant.
It said all of these were detected in managed isolation and are consistent with overseas exposure.
"We expect we will continue to see both the UK variant and South Africa variant in positive cases in our managed isolation facilities here in New Zealand as these forms of the virus become increasingly common around the world."
All positive Covid-19 tests in New Zealand are sent to ESR to attempt whole genome sequencing as part of ongoing surveillance, the Ministry said.
The testing the Ministry is aiming to better understand the new variants to "inform and refine" the overall elimination strategy.
"In particular, optimising our current stringent border processes including testing and regularly reviewing infection prevention procedures."
The Ministry has introduced further measures to strengthen the border which include a day 0/1 test and pre-departure testing for all passengers except those from Australia, Antarctica and most Pacific Islands.