Shoppers in Lewiston and across Maine and 16 other states were unable to use their food stamp debit cards for hours on Saturday, after a routine test of systems by vendor Xerox Corp. resulted in a system failure.

In Lewiston, EBT shoppers at the Shaw’s Supermarket were unable to buy groceries for about 30 minutes, Night Manager Randy Dail said.

At the city’s Hannaford supermarket, systems were down for about two hours, from 3 p.m. to 5 p.m., said a worker at the grocery store.

Xerox was testing generator backups when it encountered a failure, causing a power outage at about 11 a.m. this morning, according to a release from Gov. Paul LePage’s office. Although Xerox was able to bring back primary power, connectivity to the system in Maine and other states remained down, preventing the use of EBT cards.

“We are very sorry for any inconvenience this has caused,” said Mary Mayhew, commissioner of the Maine Department of Health and Human Services. “We have been in contact with the vendor who is working diligently to address the problem, and we expect it to be resolved shortly.”

Both the Hannaford and Shaw’s systems were fully operating as of 7 p.m. Saturday.

Shoppers left carts of groceries behind at a packed Market Basket grocery store in Biddeford because they couldn’t get their benefits, said shopper Barbara Colman of Saco. The manager at that store put up a sign saying the EBT system was not in use. Colman, who receives the benefits, called an 800 telephone line for the program and it said the system was down due to maintenance, she said.

“That’s a problem. There are a lot of families who are not going to be able to feed children because the system is being maintenanced,” Colman said. She planned to reach out to local officials. “You don’t want children going hungry tonight because of stupidity,” she said.

Colman said the store manager promised her that he would honor the day’s store flier discounts next week.

Problems persisted through the afternoon, a Xerox spokeswoman said.

“While the electronic benefits system is now up and running, beneficiaries in the 17 affected states continue to experience connectivity issues to access their benefits. Technical staff is addressing the issue and expect the system to be restored soon,” Xerox spokeswoman Jennifer Wasmer said in an emailed statement. “Beneficiaries requiring access to their benefits can work with their local retailers who can activate an emergency voucher system where available. We appreciate our clients’ patience while we work through this outage as quickly as possible.”

U.S. Department of Agriculture spokeswoman Courtney Rowe underscored that the outage was not related to the government shutdown.

Ohio’s cash and food assistance card payment systems went down at 11 a.m., said Benjamin Johnson, a spokesman for the Ohio Department of Job and Family Services. Ohio’s cash system had been fixed, but he said that its electronic benefits transfer card system was still down. Johnson said Xerox is notifying retailers to revert to the manual system, meaning customers could spend up to $50 until the system was back online.

Illinois residents began reporting problems with their cards — known as LINK in that state — on Saturday morning, said Januari Smith, spokeswoman for the Illinois Department of Human Services.

Smith said that typically when the cards aren’t working, retailers can call a backup phone number to find out how much money customers have available in their accounts. But that information also was unavailable because of the outage, so customers weren’t able to use their cards.

“It really is a bad situation, but they are working to get it fixed as soon as possible,” Smith said. “We hope it will be back up later today.”

In Clarksdale, Miss. — one of the poorest parts of one of the poorest states in the nation — cashier Eliza Shook said dozens of customers at Corner Grocery had to put back groceries when the cards failed Saturday because they couldn’t afford to pay for the food. After several hours, she put a sign on the front door to tell people about the problem.

“It’s been terrible,” Shook said in a phone interview. “It’s just been some angry folks. That’s what a lot of folks depend on.”

Mississippi Department of Human Services Director Rickey Berry confirmed that Xerox, the state’s EBT vendor, had computer problems. He said he had been told by mid-afternoon that the problems were being fixed.

“I know there are a lot of mad people,” Berry said.

Sheree Powell, a spokeswoman for the Oklahoma Department of Human Services, started receiving calls around 11:30 a.m. about problems with the state’s card systems. More than 600,000 Oklahomans receive SNAP benefits, and money is dispersed to the cards on the first, fifth and 10th days of every month, so the disruption came at what is typically a high-use time for the cards.

Powell said some grocery store cashiers had been speculating that the federal government’s shutdown caused the problem, but state officials have been assured that that is not the case.