Shopper Donna Tawhara said the Eftpos failure was announced over the loudspeaker at Pak'n Save Glen Innes in Auckland.
"[They said] it was a nationwide problem and [we] must have cash to pay," she said. "They suggested we use the Westpac ATM machine in the foyer.
"There was a long queue to get the cash. Tried my card first but it said 'Card not allowed'."
Hamish Hung was at Victoria Park New World in central Auckland during the outage.
"Kids cried since they started to get hungry, a few old ladies yelled and complained, then blamed the supermarket for poor service. Some others at the end of the queue got extremely confused then tried to call any staff to find out what was happening. It was complete chaos."
At Pak'n Save Manukau, Mark Tuifao said he had had $160 worth of groceries processed, scanned and ready to go.
"The attendant swiped my card, only for it to be timed out. This happened another two times until the attendant realised other counters were experiencing the same issues."