Cash was rarely seen in current retail conditions, he said.
"Cash is obviously an alternative... but, it can be quite hard to come by, especially in small towns where there might not be an ATM."
Harford said in an outage retailers could complete transactions manually if they were equipped to process the payments.
"Generally the systems are pretty good and we don't have many outages at all," he said.
Retailers should check in with their Eftpos providers on alternatives available to them in the instance of an outage, he said.
"It was late at night... it would have had a bigger impact if it was the middle of the day," Harford said.
A spokesman for Paymark said a response to how many transactions were affected and more information on what caused the intermittent outage would not be available today.
Last night, shopper Donna Tawhara said the Eftpos failure was announced over the loudspeaker at Pak'nSave 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 nearby to find out what was happening. It was complete chaos."
