The body of a baby found in waste being sorted at a recycling plant probably came in with a dump of commercial rubbish, the plant manager said.
The traumatised worker who found it originally mistook it for a doll or cuddly toy, but on realising it was a child dropped it instantly, the boss said.
The infant, thought to be a six-month boy, was spotted on the picking station at the Bell Waste Control site in North Lincolnshire.
Police have appealed for help in identifying the mother, who they believe is vulnerable and in need of medical treatment.
Recycling plant manager Steve Kent said the worker who found the dead baby was upset and had been sent home. He told ITV news that a colleague reported that a baby's body had been located on the picking station and they immediately stopped the machines and called the police.
"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."
Mr Kent said the worker, who had been stationed on a section picking off cardboard, wood, paper, metal and other objects for recycling, spent most of the day with the police but had since been sent home.
The waste would have come into the plant in the last two or three days and could have come from a large area, including the towns of Doncaster, Grimsby and Scunthorpe, the manager said.
A Humberside Police spokesman said: "Very little is known in terms of the circumstances which led to the baby seemingly being discarded but we are concerned that the baby's parents, in particular his mother, may need help and support following the loss of her child and as such she may be very vulnerable at this time.
"We are urging anyone who can help identify the parents of this baby or the parents themselves to come forward in order for us to make sure they get any support or medical treatment that may be required."