New York (CNN Business) Store workers at Walmart, the nation's largest retailer, are grappling with an unnerving challenge: keeping shelves stocked and giant supercenters operating smoothly while trying to stay safe from a frightening pandemic.

"The routine is up in the air. You never know what you're walking into and we are out of basic cleaning supplies [to sell]," said Gary, a Walmart employee in New York who spoke to CNN Business under the condition that his last name be withheld from this article out of fear of losing his job. His coworkers are "tired and frustrated" because they are working at a faster pace than normal and are struggling to meet overwhelming demand from jittery shoppers for groceries and household staples.

Although he is not "terribly worried" about getting coronavirus himself, he is concerned for older employees in his store.

"I want people to get the things they need, but I have to weigh that against keeping my people safe," said one Walmart employee in Arizona who also spoke under the condition of anonymity out of job concerns. This employee is concerned most about riots breaking out in the store. "Customers are clearly scared, panicked, and very on edge."

A Walmart spokesperson said that "while this is a challenging time, people have remained relatively calm," adding, "we're thankful for the way our associates have pulled together."

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