The Constabulary says officers were called to the facility on Ipswich Road shortly after 3pm on 14 May.
The death is being treated as unexplained and an investigation has been launched, the police say.
Detective chief superintendent Eamonn Bridger of Suffolk Constabulary said: “We understand that this would have been a very distressing experience for the mother of this baby. Our current priority is to ensure she receives the care and assistance she requires and we would urge that she contacts us so we can help.
“I am making a direct appeal to this baby’s mother. There is no doubt that she may be frightened but it is very important that we reach her or we speak to someone who might know her.
“We would urge the mother to speak to a healthcare professional or to attend a hospital”
“We believe the baby was born very recently so the mother may require medical assistance and we would urge her to speak to a healthcare professional or to attend a hospital.
“At this time, our priority is ensuring she receives the care she needs and the right support.”
A police cordon remains in place at the Needham Market site while investigations are carried out.
Needham Market
The baby girl is believed to have been less than 24 hours old.
A spokesperson for Sackers said: “First and foremost we want to send our condolences out everyone involved in this tragic situation.
“Our recycling sorting facilities are so thorough that we believe the baby was found very quickly once it was at our Needham Market site.
“Our main priority now is to support our staff members who were involved in this incident and assist the police with their investigation. Therefore, the site will be closed until further notice.”
Established around 1929 in Ipswich, Sackers operates a scrap metal site in Claydon and the recycling facility at Needham Market.
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