The Prime Minister says genome sequencing hasn't linked the latest Covid-19 community cases to anyone in managed isolation.

The three new community cases of Covid-19 announced yesterday are the UK strain of the virus, Jacinda Ardern told Morning Report.

Sewage tests will be undertaken in Auckland and Taranaki today to see if it can detect any traces of Covid-19, Ardern said.

Lockdown restrictions in Auckland started at midnight and will last three days, although the government will revise the status daily. The rest of the country is under alert level 2.

Police say Auckland boundaries will be set mostly in the same locations as the last time the city was in alert level 3 in August, to ensure there is no non-essential movement through the region. Auckland mayor Phil Goff said travel exemptions would be made for those needing to get home.

Under the restrictions, Aucklanders need to stay home, and should also work from home if possible.

Non-essential shops will close, and schools and early childhood centres will only be open to children whose parents cannot work from home.

Australia has suspended its quarantine-free travel corridor. People flying from New Zealand from Monday to Wednesday will be required to quarantine for 14 days.