Shelves are empty — but when will they be restocked?

Stores are racing to replenish depleted shelves and to calm shoppers anxiously preparing for coronavirus disruptions, but are having trouble meeting the heightened demand.

“Hand sanitizer is going to be very difficult to have 100 percent on stock on for some time,” Walmart CEO Doug McMillon said at a White House press conference Friday. “We’re still replenishing it and shipping it, but as soon as it hits the stores, it’s going.”

McMillon said a stressed supply chain was responsible for the racks bare of paper product, water, and cleaning supplies.

“All the retailers have been working hand-in-hand with the suppliers to bring that to the markets as fast as we can,” he said.

Retailers are rerouting supplies to areas of the country that need it most. To prevent hoarding, they’re applying or giving store managers power to set limits on the number of individual items a customer can buy in a single trip.

“As always, our focus is to have merchandise available for our members at low warehouse prices,” a Costco spokesperson told NBC News.

In a statement, Target said its team is “working around the clock to make sure that the products you want are available when you need them. As demand for cleaning products, medicine, pantry stock-up items and more remains high, we’re sending more products to our stores as quickly as possible.”

Some stores said they’d been preparing for the possibility of this outbreak leading to increased purchase behavior and were poised to switch to additional supply options and modified operations.

Mabrie G. Jackson, director of public affairs for Texas supermarket chain H.E.B. tweeted the retailer “has been preparing for coronavirus for several months and we are in a strong position to keep replenishing our shelves. Customers should not panic, we have the ability to restock shelves and encourage our customers to remain calm.” The store also announced it was temporarily reducing its store hours at most locations.

The pace of restocking and whether the supplies last long will depend on customer behavior, and how much inventory each store’s wholesaler or supplier has in the pipeline, retail grocery consultant Joe Walsh said.

“It’s a store-by-store case, but for a majority of chains and independents they will replenish from their wholesaler immediately,” he said. “Every case of bath tissue currently produced in pipeline, at a wholesaler or a warehouse, all those are spoken for.”

The real crunch is not the next shipment to restock after this week’s panic buying, but the one that comes after, said Walsh.

“They all have to buy from the same five to six places,” he said, referring to the manufacturers. “We’re going to see limits, allocations, restrictions…if they get five cases a week of Charmin, they might be able to buy 10.”

Customers should brace for the possibility of long lines, limits on the number of items they can purchase, the disappearance of discounts for high-demand items, and the possibility of price increases, said Walsh. And if stores cut hours excessively, or if hourly employees such as shelf stockers or cashiers self-quarantine and don’t show up for work, lines could grow.

Logistics experts said they expect stores will quickly figure out how to cope with the surprise spike in purchasing.

“The real reason for things running out is this ‘run,’” by shoppers, Ananth Iyer, a professor of operations management at Purdue University, said. “They believe they need more of it and are not sure if it will be available when they want it. Retailers, given demand, will find a way to generate supply.”

But smaller stores in particular may have to pay more if they want to get resupplied sooner. Stores could try to convince shoppers to take a smaller order now and sign up for the rest of the order next week or sign up for weekly delivery, and get more shoppers to buy groceries online, Iyer suggested.

“That option might calm people down,” he said.