Updated

Authorities in Texas on Sunday said a 15-year-old migrant boy walked out of a migrant shelter in southern Texas and has not been found.

The teen walked out of the Casa de Padre shelter in Brownsville on Saturday at 3 p.m., a spokesman from the Southwest Key Programs told Fox News.

The center is considered the largest in the country and was a former Walmart. The center houses boys from 10 to 17, many of whom arrived at the border without parents.

Jeff Eller, a spokesman from Southwest Key Programs, said workers at the licensed child care center cannot stop a child who wants to leave.

“We are not a detention center,” he said. “We talk to them and try to get them to stay. If they leave the property, we call law enforcement.”

The New York Times reported that there are about 1,500 boys at the facility. Eller told the paper that children leave “from time to time,” but less than 1 percent.

Since the White House announced its zero tolerance policy in early May, more than 2,300 children have been taken from their parents at the U.S.-Mexico border, resulting in an influx of young children requiring government care.

By law, child migrants traveling alone must be sent to facilities run by the U.S. Department of Health and Human Services within three days of being detained. The agency then is responsible for placing the children in shelters or foster homes until they are united with a relative or sponsor in the community as they await immigration court hearings.

But U.S. Attorney General Jeff Sessions' announcement last month that the government would criminally prosecute everyone who crosses the U.S.-Mexico border illegally has led to the breakup of migrant families and sent a new group of hundreds of young children into the government's care.

Tony Martinez, the mayor of Brownsville, raised questions about the facility in an interview with the paper.

“If the facility was such a great idea, why are they trying to get out?” he said. “Most of the people that escape, they escape from jails. They escape from prisons, because it’s not a fun place to be at. I can just imagine what might be going through that young man’s head, at 15 years old: ‘What am I doing here?’”

Fox News' Bryan Llenas and The Associated Press contributed to this report