A Japanese convenience store chain has suspended the sale of rice balls, or onigiri, and other deli items at 1,600 stores after it found that staff had faked their expiry dates.

Staff at some stores extended expiry dates by not sticking labels on the dishes until an hour or two after they were prepared. Others relabelled the items with false dates after they were put on sale, Ministop found.

The misconduct was reported at 23 stores across the country, including in major cities like Tokyo, Kyoto and Osaka.

The chain has paused onigiri sales at most of its outlets since 9 August, and on Monday extended the pause to other deli items, for an "emergency investigation".

"We sincerely apologise for the significant inconvenience caused to our customers who have supported Ministop's handmade onigiri and handmade bento boxes," the company said in a statement on Monday.

Customers have not reported any health issues so far, it added.

Convenience stores or konbini are part of daily life in Japan, where people - especially commuters - stop by for affordable and filling meals and last-minute groceries and banking errands.

Onigiri is popular among customers who want grab-and-go meals as the rice balls are easy to carry - wrapped in nori or dried seaweed and filled with protein like tuna salad or cod eggs.

Ministop operates more than 1,800 stores across Japan. Its focus on fresh food – with hot meals prepared on site – sets it apart from the larger chains.