A 6-month-old baby girl was found dead in a dumpster in South Los Angeles … and her mother is in custody as police investigate the infant’s death as a homicide.

The baby was discovered in the trash receptacle late Monday night in South L.A. … though LAPD says the child had been left there sometime in the previous 24 hours.

Cops say firefighters responded to the scene and took the baby to a nearby hospital … where she was pronounced dead.

The LAPD tells TMZ … officers received a call about a death investigation late Monday for an infant female found in a trash can.

LAPD’s Juvenile Division is investigating the child’s death as a homicide. Officers have already determined the child was not homeless, and the crime is not gang-related.

ABC7 reports they had a journalist on the scene who saw the baby’s mother placed in handcuffs and taken away in a police vehicle.

The outlet also reports they spoke to a couple who said the baby might be their granddaughter. They claimed the daughter gave their grandkid to the child’s father around 6 PM Monday, and the family hadn’t heard from him.