Prime Minister Jacinda Ardern this afternoon announced it will be mandatory for anyone over the age 12 to wear a mask when visiting essential services.
It comes as there are now seven community cases of Covid, and officials expect up to 120 cases.
From 11.59pm tonight staff and customers must wear masks at essential services, such as supermarkets, pharmacies, dairies and service stations.
New Zealanders must also wear masks at bus terminals and in taxis.
Police Commissioner Andrew Coster said police could issue infringements to those not wearing a mask under new alert level 4 rules.
Arresting people was theoretically possible, Coster said, but police did not want to result to that.
"We know that with Delta, the risks are higher, so we've leaned towards enforcement more than we did with the earlier lockdowns, and we will monitor how that's going," Coster said
University of Auckland Aerosol Chemist Dr Joel Rindelaub said expanding mask mandates from public transit to other indoor areas was a wise move.
"Indoor environments are high-risk locations for Covid-19 transmission and super-spreader events, due to their decreased air ventilation," Rindelaub said.
He said because of the increased spread of the Delta variant, the US Centre for Disease Control recently renewed its mask use recommendations.
"It makes sense for New Zealand to use what other countries have learned to help shape protection strategies against the ever-changing coronavirus.
"The Delta variant is a new threat, and we need to take new action to help fight it," Rindelaub said.
University of Auckland Faculty of Medical Health Sciences Professor and Pacific associate dean Colin Tukuitonga said one more case of Delta could infect up to nine people and then those nine would infect another nine.
"Covid-19 tends to affect people with underlying medical conditions like diabetes, obesity and respiratory conditions," he said.
Tukuitonga - also a Pasifika Medical Association (PMA) member - said Pacific communities had high rates of those underlying conditions which put them at a higher risk so that was why it was of a particular concern.
"Where you have a virus that spreads quickly like the Delta variant, the conditions of our people, the housing and overcrowding, means it would spread like wildfire. That's why we want to get on top of this as quickly as possible.
"We've done this before and we've been successful and I'm pretty sure if we do it again, we'll come out good as well."