As the frantic search continues for a missing 11-year-old boy in New York City, police say they have taken his mother into custody and that she denies having a child. 

The 50-year-old woman's apartment in Brownsville, Brooklyn, has been sealed as the NYPD investigates what happened before officers conducted a wellness check and the boy was nowhere to be found.

When officers arrived, she told them she did not have a child and let them inside the apartment on Howard Avenue, police said, after the City Administration for Children's Services initiated the wellness check Thursday.

A K-9 detected blood inside the refrigerator, according to police sources. An ACS investigator was also on the scene looking into an alleged child abuse case.

The woman was led out of the building in handcuffs and taken to Brookdale Hospital for a psychiatric evaluation. She has been uncooperative with investigators, police sources said.   

Boy was smaller than others his age, neighbors say

Neighbors said they have not seen the boy in six to eight weeks. They said he looked much smaller than other children his age. 

"I remember even seeing him sucking a bottle," one neighbor said. "I thought he was a baby." 

Others said the mother and child were living in the apartment for about four years. Some said they would hear screaming coming from inside and that the boy was timid outside. 

"He was usually quiet. She was always holding his hand," Monique Minter said. 

It was unclear when the boy was last in school. A City Department of Education representative could not confirm if the boy was enrolled in the public school system due to privacy concerns. 

CPS went to apartment in September

The woman has no prior history with ACS, police sources said, but Child Protective Services responded to her apartment for an undefined allegation in late September. It was unclear if they made contact with her. 

"The safety and well-being of New York City's children is our top priority.  As soon as this family came to our attention, we launched an investigation with the NYPD," an ACS spokesperson said in a statement. 

The boy's whereabouts are unknown at this time. 

Anyone with information is asked to call the NYPD's Crime Stoppers hotline at 1-800-577-TIPS (8477), or 1-888-57-PISTA (74782) for Spanish. You can also submit a tip via their website. All calls are kept confidential.