Both girls are 17. One was hospitalized and the other was being questioned at a police precinct, authorities said. The medical examiner's office was performing an autopsy on the apparent human remains found inside the bag.
The girls were shopping at a Victoria's Secret lingerie store in midtown Manhattan, said police, who were called to the scene. Authorities are trying to determine if one girl gave birth in the store, or if she had been carrying the remains with her. She apparently told detectives she delivered a day earlier, but didn't know what to do with the remains, police said. It wasn't clear whether the fetus was alive or dead when delivered.
Victoria's Secret is owned by Columbus, Ohio-based Limited Brands. A spokeswoman for the company referred calls to the NYPD.
Police are also investigating whether the girls had actually stolen anything from the store, or whether they will face criminal charges.
An NYPD crime scene unit van stationed at the store left a few hours after the 1:30 p.m. incident after collecting bags of evidence. The store was open for business and filled with customers from around world. A single marked police car stood before the front entrance that faces Herald Square at 34th Street.