Costco Wholesale Corp. late Wednesday said that its March net sales rose nearly 12%, including a 48% jump in online sales, providing a window into stockpiling as the coronavirus pandemic began to keep most of the U.S. population confined to their homes.

Net sales rose to $15.49 billion from $13.87 billion in March 2019, Costco COST, -0.86% said. Combined, store sales in the U.S., Canada and other countries where Costco has a presence were up 9.6%, the retailer said. The report spanned the five weeks from March 2 to Sunday.

Costco reported an 8% increase in January net sales and a 14% increase in February net sales. That month, when the first U.S. cases of COVID-19 surfaced, e-commerce sales rose nearly 23%. By mid-March, major cities across the U.S. issued orders to self-quarantine and businesses deemed not essential shut down.

“Costco is among the strongest retail brands and there is no better example of the company’s unique position than the flood of visitors in the early stages of the coronavirus,” Ethan Chernofsky of retail intelligence company Placer.ai said in a report ahead of the March sales release.

“Costco has performed exceptionally well during normal periods, and the pandemic has shown that they can still drive strong results — especially compared with other retailers — during difficult times as well,” he said.

Costco shares fell nearly 4% in the extended session, after ending the regular trading day up 0.8%. The stock has gained 24% in the past 12 months, contrasting with losses around 5% for the S&P 500 index SPX, -1.11% in the same period.

Going into the report, Placer.ai had detected some slowdown in foot traffic for Costco stores as well as Walmart Inc. WMT, -1.02% and Target Corp. TGT, +0.82% stores by late March as social-distancing efforts and e-commerce took a firmer hold across the U.S.

The retail industry overall lost 46,200 jobs in March to furloughs and layoffs in the wake of store shutdowns related to COVID-19, according to the latest U.S. government data, but a trade group has warned the unemployment will rise much more as the store closures continue.

The retail workforce could drop by two million by May, The National Retail Federation has said.