Covid-19 Response Minister Chris Hipkins does not know how many young people have received surprise invitations to book in for a vaccine.
Those over 65 or with underlying serious health issues are currently being vaccinated.
However, some people in their 20s are being contacted by text to book their vaccine and say they have no idea why.
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Hipkins said he had heard of reports of this, but has not been advised it is a systemic problem.
The Health Ministry is looking into it, he said.
Just over 705,000 New Zealanders had received a first dose and more than 440,000 had received a second dose by yesterday.
In group 3, 206,406 have had a first dose, and 91,477 have had a second dose.
On Tuesday, Hipkins warned that vaccine stocks will be at "almost zero" by next Tuesday, before the country receives another shipment.
As a result, the Government is banking on another shipment of 150,000 doses arriving next week to avoid running dry.
It has also announced that all up, the country is due to receive one million doses from Pfizer this month.