Single-use plastic carrier bags will be phased out of all South Island Countdown stores from early October.

The supermarket chain is adding 67 stores to its countrywide phase-out from October 8, including 15 in Christchurch.

The move meant 85 per cent of the company's 180 stores would no longer offer the bags, as part of an aim to have all stores join in by the end of 2018.

Countdown's general manager of corporate affairs and sustainability Kiri Hannifin said their stores used an average of 6000 bags every day.

"The faster we can make this change, the sooner we can make a difference for the environment."

Since Countdown began phasing the bags out in May, 22.5 million bags had been removed from circulation.

Some stores had experienced teething issues, with customer taking shopping baskets and trolleys with them.

Countdown Orewa has reportedly been left with just 10 shopping baskets, down from 200, after the store stopped providing single-use plastic bags last month.

The stores offered reusable bags, a thicker 15-cent plastic bag - designed to be used 20 times - and the $1 Bag-For-Good for those who did not have their own bags.

All Countdown stores in Ashburton, Napier, Hastings, the Waikato region, Auckland's North Shore and Timaru would also make the move away from plastic on October 8.

Hannifin said having the entire South Island network phase out single-use plastic carrier bags was a massive milestone for the business.

"[It] will mean every one of our South Island Countdown stores is supporting customers to make the move to reusable bags. The end of single-use plastic bags at our checkouts and online is in sight."

Customers were adapting well to the changes and adjusting their shopping habits, even in stores where bags are yet to be phased out, Hannifin said. 

"Already, we have seen a 17 per cent decrease in the amount of plastic bags our customers are using when they shop with us.

"Making reusable bags the norm will have long-lasting benefits for New Zealand's environment.

"One of the reasons the phase out is going so well is that our customers have really got behind this move and we hope this will continue when these further stores make the change."

In August, the Government announced single-use plastic bags would be banned in New Zealand, and be phased out over the next 12 months.