Some Canterbury and Auckland supermarket shoppers can now bring in their own containers in a bid to reduce plastic.
Countdown is trialling the initiative on food sold over-the-counter, including deli, meat and seafood products.
Spokesperson Kiri Hannifin says food safety is the top priority.
"We're pretty sure we've got an excellent process - we're just going to test it out in these 18 stores to make sure it works for our customers, then we're good to go."
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Stores across Canterbury, as well as Auckland's Mt Eden and Mt Roskill, are taking part in the trial, which follows a similar move by Foodstuffs supermarkets.
Countdown is confident food safety standards will be met.
"We're going to give it a quick clean ourselves with food-safe detergent with a bit of water, wash and dry it and then we're going to use it and give it back to the customer," said Hannifin.
If successful, the initiative will be rolled out across the country in a matter of weeks.
"We've taken out well over 100 tonnes of plastic just from produce - we're looking at all of it, including those little barrier bags as well."
Supermarkets have phased out single-use plastic bags over the past few months.