New Zealand announced Friday it will ban disposable plastic shopping bags by next July as the nation tries to live up to its clean-and-green image.

Prime Minister Jacinda Ardern said New Zealanders use hundreds of millions of the bags each year and that some of them end up polluting precious coastal and marine waterways.

Ardern made the announcement at a beachside cafe and said it was the single biggest issue that school children write to her about. She had three children read aloud their letters, before she led several dozen children on a cleanup along the beach.

New Zealand's two main supermarket chains had already announced their own plans to phase out plastic shopping bags by the end of this year. Countdown made the move first and was matched by New World after it surveyed its customers.

A number of countries and states have introduced bans or restrictions on single-use plastic bags, including France, Belgium, China, Hawaii and California.