There have been warnings that retailers could face six-figure fines, although a court would need to determine a penalty if a prosecution was successful.
However, the ministry has pointed out it wants to focus more on working with businesses to encourage compliance.
In the event that someone contacts the ministry to tell them about a breach, officers would contact the business and work with them to find out why they hadn't stopped giving out banned bags.
The ministry also plans to begin random retail precinct audits to assess levels of compliance and advise retailers where changes are required.
Sage said the six-month phase-in period had given retailers time to make the switch, and as at the end of last year, supermarkets were no longer offering single-use bags.
New Zealanders appear to have adopted the change early. Survey results show more than 80 per cent of shoppers were bringing their own reusable bags with them as at last September — up from just over half of shoppers a few months before that.
"I expect people to comply because New Zealanders want to do the right thing," Sage said.
"Banning these bags mean that we will be saving tens of millions of bags from going to landfill or getting into rivers, streams and into the ocean, protecting our marine life, seabirds and marine mammals. It also means that New Zealanders who are proud of our clean, green image are helping to protect that image."
Despite single-use plastic bags making up just a fraction of the plastics polluting our environment, Sage said the Government wasn't considering any other bans on such single-use items.
But she called the move "symbolic" — and said it had started a new conversation about how single-use plastics could be phased out.
Meanwhile, a researcher has warned that consumers should not use plastic for packing or storing food because toxins can leach into it.
Massey University environmental anthropologist Dr Trisia Farrelly said a recent study suggested people were consuming about 2000 tiny pieces of plastic every week — that's equal to five grams, or the weight of an Eftpos card.
Farrelly said consumers were already seeking out food and drink containers that were free of Biphenol A, or BPA. "Unfortunately, industry has found loopholes by using alternatives in 'BPA-free' bottles by simply using other bisphenols — such as BPS — which are even more harmful than BPA."
Farrelly further called for new industry guidelines around using recycled plastics.
"Never use recycled plastic for food packaging or storage unless you undertake a number of stringent steps: an improved sorting process, a super clean recycling process, creating functional barriers between your food and food packaging, and ban toxic chemicals used in food packaging," she said.
"The global plastic pollution crisis is not just about the environmental impacts anymore, it's not just about climate change anymore, it's also about our health – and the health of the soil and the plants and animals we eat, the water we drink and the air we breathe."
