A post-mortem examination on a child's body found at a waste plant in Scunthorpe confirmed that the body was that of a newborn boy.
The body was discovered by a worker at Bell Waste Control in Scunthorpe, North Lincolnshire, on Wednesday.
The baby was found as a member of staff worked on a section picking off cardboard, wood, paper, metal and other objects for recycling.
He originally mistook it for a doll or cuddly toy, but on realising it was a child dropped it instantly.
Recycling plant manager Steve Kent said the baby could have been discarded in a load of commercial waste, possibly from a factory or office.
"The guys have obviously stopped the plant and we have notified the police immediately," he said.
"He was quite distressed and he immediately dropped it. We stopped the plant and went through the process with the police.
Humberside Police said a post-mortem examination confirmed the infant was a newborn boy.
The cause of his death is yet to be established and further tests will be carried out, police said.
"The teenage girl is now receiving the necessary care she requires and further inquiries into the circumstances of what happened will be made in due course," a police spokesperson said.