Phoenix, Arizona: Phoenix police spokesman Vincent Lewis said the newborn was reported to police at the online retail giant’s facility on Wednesday evening.
Homicide detectives are working to determine if any crime was committed at the facility, he said.
Police have identified the mother, who is co-operating with the investigation.
In a press conference on Thursday, Sgt Lewis refused to publicly name her or say whether she is employed at the distribution centre.
“But, again, the restroom was located inside of a secured Amazon facility,” said Sgt Lewis, who refused to speculate on what charges the mother may face.
He said that investigators are looking into whether the child was born in the toilet, adding that the infant appeared to have only been there briefly.
“It had been there some time,” he said, adding, “very recent, same day”.
“It appeared to first responders that the baby was full term, or close to that,” the spokesman said, adding that she could not be resuscitated by medics from the city’s fire department.
According to local media, the child was discovered in a rubbish bin by a maintenance worker.
Amazon said in a statement: “This is a terribly sad and tragic incident.
“We are working with local authorities to support their investigation.
“The safety and wellness of our team is our top priority.”
The company’s massive distribution centre on the city’s southwest side is one of several Amazon sites in metro Phoenix.
Under Arizona law, mothers can anonymously leave unharmed newborns at designated “safe haven” locations.
They include hospitals, ambulances, churches, on-duty fire stations and adoption agencies. The baby must be under 72 hours old and given to a person.
The law, which was passed in 2001, also states the mothers who follow those instructions will not face prosecution.