Masks are now required at Alert Level 4 in all public gathering spaces, including supermarkets, service stations, pharmacies and dairies.
The mask mandate extends to public transportation, including departure points such as depots and bus stops, and also health care facilities.
A police spokesman said things had gone reasonably well for the first day of compulsory mask wearing in Dunedin.
"We don’t think we have been called to many, if any, incidents of people refusing to wear [masks]."
The Foodstuffs chain, which includes Pak’nSave and New World, said it would turn people away if they were not wearing a mask.
Foodstuffs had a "no mask, no entry" policy, South Island chief executive Steve Anderson said yesterday .
The supermarkets would use a mixture of staff and security guards to monitor whether shoppers were keeping to the rules.
Rival chain Countdown said staff and shoppers needed to wear masks in its stores, but it would leave enforcement to police.
Countdown general manager of corporate affairs, quality, safety and sustainability Kiri Hannifin said staff were not suddenly going to become bouncers at the door.
"It’s not our job to enforce it."
Police would be called if any customers became angry or aggressive, she said.
Observations of Dunedin supermarkets yesterday morning showed the vast majority of shoppers were complying with the mask mandate.
There were 32 people queuing at Gardens New World in North East Valley and 13 in a queue at Countdown Dunedin Central, all of whom were wearing masks.
However at Pak ‘n Save Dunedin there were two unmasked shoppers from a queue of 52 people.
It was unclear if these two shoppers put on a mask to enter the store.
Dundas Corner Dairy owner Mabel Ma said mask use was near universal in her store yesterday.
Regionally mask compliance was also clear to see.
Supermarkets in Alexandra, Cromwell, Oamaru, Invercargill and Balclutha all had the majority of their customers wearing masks.
In Wanaka a staff member at the Ardmore St Four Square said they had one elderly man who refused to wear a mask, but otherwise had not had problems.
A spokesman for the Department of the Prime Minister and Cabinet said as well as the mandatory mask locations, people were encouraged to wear masks whenever they left the house.
A southern academic said mask mandates could go even further, particularly to protect essential workers.
Prof Nick Wilson, of the University of Otago’s public health department, said New Zealand had been well behind many other countries when it came to mask initiatives.
"My colleagues and I have been very disappointed that masks weren’t built into the alert level system many months ago."
The mask mandate should be extended further to essential workers working indoors close to other people, he said.
In many essential workplaces, such as factories and food-processing plants, it was not possible for workers to socially distance 2m.
For other workplaces social distancing by 2m may still be insufficient to stymie the spread of Covid-19 because of poor ventilation.
People walking in their neighbourhoods may wish to wear a mask out of caution, particularly if using footpaths that did not allow for 2m social distancing, he said.
