Companies began sending in products to restock Amazon’s warehouses. But with attendance down and more items coming in, workers could not replenish the supplies fast enough. Trucks backed up, waiting days to be unloaded. The company offered shift after extra shift, raised wages $2 an hour and paid double the hourly rate for overtime. It eventually announced that it would hire 100,000 new workers.

In mid-March, Amazon stopped accepting new shipments into its warehouses that were not for priority products, like health care and baby supplies.

On March 16, Jeysson Manrique, an employee of a delivery company that contracts with Amazon, woke up with a fever. His body ached. He called his supervisor to say he was sick. Mr. Manrique, 29, was asked to text a picture of his temperature on a thermometer. He couldn’t find one, so he went in for his shift at an Amazon facility in Queens. Amazon said it was investigating the situation with the contracting company because its policy requires employees stay home if they feel sick.

Two days later, Mr. Manrique’s father-in-law — they live together in a house with other members of the family — was sorting packages at the same facility when his doctor called to tell him that he had tested positive for the coronavirus. His father-in-law shared his test results with his supervisors and went home.

When the warehouse closed for cleaning, he was the first publicly known case inside Amazon’s vast warehouse operations in the United States. Mr. Manrique joined his father-in-law and other members of the household in quarantine without venturing out for a test.

On March 23, rumors circulated at the Queens facility that another employee had tested positive. Hours later, there were whispers of a third. The building was shut down March 24 and March 25 for deep cleaning. The company had also begun instructing warehouses to keep employees apart, staggering when they arrive and canceling group meetings at the start of shifts.

Some workers said they were still handling products that were helpful but hardly critical. One warehouse employee posted a picture on social media of moving large boxes, including a Power Wheels Jeep that a child can ride, with the hashtags #SoManyPingPongTables and #TreadmillsAreEssentialProductsApparently.