ROMEOVILLE, Ill. — Brandon Williams arrived at an Amazon fulfillment center here, about an hour outside of Chicago, around 7:30 a.m. on Wednesday, one of thousands across the country who turned up for the company’s first Jobs Day. While he appeared to wilt slightly during the five hours he waited before an M.C. summoned him for a tour, his enthusiasm did not wane.

“What’s not great about a company that keeps building?” he said, seated in a huge tent the company erected in the parking lot as a kind of makeshift waiting room.

The event was a vivid illustration of the ascendance of Amazon, the online retail company that, to a far greater extent than others in the tech industry, has a seemingly insatiable need for human labor to fuel its explosive growth.

Like other tech giants, Amazon is recruiting thousands of people with engineering and business degrees for high-paying jobs. But the vast majority of Amazon’s hiring is for what the company calls its “fulfillment network” — the armies of people who pick and pack orders in warehouses and unload and drive delivery trucks, and who take home considerably smaller incomes.