The New Zealand Retailers Association says 100 million bags have been taken out of circulation since a reduction target was set in 2004.
Association spokesperson Barry Hellberg says latest research shows that shoppers are now taking on average 5.8 bags, down from 6.5 bags, 12 months ago.
Mr Hellberg says the industry is on target to meet its 20% reduction of plastic bags by July this year.
He says plastic bags account for less than 0.2% of waste to landfill and consumers need to remember to use their reusable bags while shopping.
But Green Party co-leader Russel Norman says the reduction is not enough and further measures should be taken.
He says there is no incentive or reward for consumers to use recyclable bags.
Mr Norman says the introduction of a levy would create a financial incentive for customers to bring their own bags.
He welcomes a move by South Australia to ban all plastic bags.