In today's update, Ardern reminded the country alert level 4 was still active as preparations are made to move to level 3.
She said while the vast majority of people were complying with lockdown measures, some still continued to breach the rules.
“While I know there will be things we are all looking forward to under alert level 3, we must not risk the gains we have made or that many New Zealanders have made sacrifices for over the last four weeks," she said.
Police figures showed there were 4,128 breaches, 433 prosecutions, 3,580 official warnings, and 115 youth referrals since 6pm yesterday.
“Each and every one of these people involved in breaches risks undoing the work of others,” Ardern said.
The Prime Minister also cleared up some questions about the move to level 3.
She said Kiwis returning from overseas would still have to isolate in Government-provided facilities.
2,403 people were in such facilities, mostly hotels.
Ardern said this was an intrinsic part of the coronavirus response and there was no clear end point of the process.
Work on major infrastructure projects would continue in level 3, such as the Auckland rail link and non-essential road maintenance.
Strict health and safety guidelines would be implemented on sites to protect workers.
Ardern gave special thanks to cleaners who were working to prepare businesses and Government services for alert level 3.
Cleaners were vital to businesses, courts and police stations, to create and maintain a safe environment for returning workers, she said.