AUBURN, Mass. » A 2-year-old girl died while in foster care and another was in very critical condition Sunday after the pair was found unresponsive at a home.

Worcester County officials said they were conducting an autopsy, and police were still investigating what happened at the Auburn home.

District Attorney Joseph D. Early said at a news conference Sunday that the children’s foster mother called 911 at 12:23 p.m. Saturday, reporting two children were unresponsive. When emergency officials arrived, they performed CPR on one girl who was unconscious. Lifesaving measures were performed on the two girls, who Early said were both around 2 years old.

They were transported to UMass Memorial Medical Center in nearby Worcester. One girl was pronounced dead a short time later.

One girl remained in "very critical" condition Sunday evening.

Names are not being released pending notification of the toddlers’ biological parents.

One other foster child and three biological children of the mother were removed from the Pheasant Court home.

Early called the situation "a very difficult case." A police chief said that officials were "very familiar" with the mother, but Early told reporters there was no initial sign of abuse and no one has been taken into custody. He added that the mother has been cooperating with authorities.

An air quality test performed on the home came back negative, Early said, ruling out carbon monoxide poisoning.

Department of Children and Families spokeswoman Andrea Grossman said in a statement that the DCF is working with law enforcement and conducting its own investigation.

Neighbors said they heard the woman who lives in the home screaming outside at about 1 p.m. Saturday and saw the girls being taken away in an ambulance.

Sonia Guzman lives across the street. She told reporters her daughter rushed over to help the woman, who was holding an uninjured 6-month-old baby in her arms.

"She’s a really good mother with the kids," Guzman said. She added that the woman was planning to adopt some of her foster children.

On Sunday afternoon, neighbors placed a bouquet of flowers, candles and two stuffed toys outside the home.

Elizabeth Guyton, a spokeswoman for Gov. Charlie Baker, said Sunday he "is deeply saddened to learn of this tragic situation and is in constant communication with leadership at DCF and public safety about their ongoing investigation."