The federal government has transferred hundreds of undocumented immigrant children to a makeshift detention center in Arizona following a surge of crossings from Central America. Over 1,000 children are reportedly being held at a warehouse in Nogales, some sleeping in plastic containers. Around 300 children caught near the Texas border crossing with Mexico were moved to Nogales over the weekend. Cyndi Whitmore of the Phoenix Restoration Project, an immigrant rights group, voiced concerns over the children’s conditions.

Cyndi Whitmore: “I think that the volume that we’re seeing right now is pretty unprecedented and that they’re putting together some last-minute and transitional shelters and processing areas, which of course we have concerns about whether or not those facilities are adequate, as we’ve already seen that the facilities in which the family units were being held were very inadequate, and to the point of being inhumane.”

After their detention at the Nogales site, the children will be sent to one of three U.S. military bases in Oklahoma, California or Texas. The Department of Homeland Security says it’s seeing a surge of migrants fleeing poverty and violence in Central America. Up to 90,000 unaccompanied minors are expected to cross into the United States this year. Last month, U.S. officials dropped off hundreds of undocumented immigrants at a Phoenix bus station. They were told to find their relatives around the nation and then report to the nearest federal immigration center. Advocates have accused the government of stranding the migrants with no food or money in sweltering heat.