MINNEAPOLIS — Long lines formed at Target stores across the nation Saturday after the retail giant’s cash registers quit working, and shoppers reacted with amazement and frustration.

On Twitter, Facebook and other sites, shoppers posted experiences about long waits at checkout lines on Saturday. In some places, employees blocked doors into the store.

On Twitter, the Minneapolis-based retailer posted messages from social media, including @Target and @AskTarget.

“We’re aware that guests are currently unable to make purchases at Target stores,” Target Corp. spokeswoman Jenna Reck said. “Our teams are troubleshooting now and we apologize for the inconvenience.”

Reck said the problems were limited to stores, and that Target.com was not affected.

At the downtown Minneapolis store, shoppers looked patiently resigned as they waited to buy pop, toothpaste, Father’s Day cards and other items as the line of about 50 inched forward.

“I thought the self-checkout would be quick, but it doesn’t look like it,” said Margaret Wainwright of Minneapolis.

Trevor Nelson of Lake Elmo, who works for a concert promoter presenting a show at the Armory Saturday night, had been dispatched to buy bottles of juice and other refreshments requested by the band. Target, with its parking ramp and adjacent liquor store, had seemed a convenient place to get everything.

“This is — this was — going to be the perfect stop,” Nelson said, wondering if he’d still get free parking in the ramp if he wasn’t able to make the $20 minimum purchase.

About half an hour later and 20 feet closer, Nelson heard that customers who made it to the registers were getting parking passes as well as $5 gift cards.

“Woo-hoo,” he said with a touch of sarcasm. “This is my lucky day.”

Cashier Jodi Chu of Minneapolis was smiling, even though it was only her second day at Target and her first time working at a cash register. Occasionally a product could be scanned successfully, but most attempts brought up error messages. For those, she had to laboriously enter prices, tax and other information manually.

“I got really good training,” Chu said. “My trainer was so good — she was so good.”

There were reports around 2:30 p.m. that some stores, including Richfield’s, were able to complete sales as employees manually worked through glitches at the registers. Employees at the store had tried to placate shoppers with free Starbucks and popcorn, saying the problems began around 1 p.m.

The website downdetector.com showed reports of an outage in major cities, including the Twin Cities, Los Angeles, Atlanta, Chicago, New York City and Baltimore. Reports began spiking around midday. Target operates about 1,850 stores nationwide.

Danielle Wilson’s Twitter post around 1:40 p.m. CDT summed up many frustrated shoppers: “Nothing like loading up your @Target cart on a SATURDAY for them to announce that ALL registers are down (an hour now) My veggies are melting. apparently it’s a global issue. Is it the Apocalypse?!?! All those indulgent wants left behind.”

The retailer experienced a similar glitch in June 2014, which it blamed on a defect with a network device that affected its point-of-sale systems. In that case, the problem happened on a Sunday evening and was resolved within hours.

A system failure during the peak of weekend traffic could have broader implications for sales — and possibly its image.