Harris also demanded immediate reunification of separated families, raising concern over their detention in a 'typical prison setting,' after her visit to the Otay Mesa Detention Facility near San Diego in California yesterday.
"The mothers I spoke with today who have had their children taken, they think that they're alone. We need to remind them and everyone else that they are not alone and that we all stand with them," she said.
"This is outrageous. This is clearly a crime against humanity that is being committed by the United States government and we have to stop it," a visibly upset Harris told a crowd of several hundreds outside the detention centre.
The Democratic Senator said separating children from their parents was unacceptable and charged that these women, who have fled violence in their countries, were being treated by the US government as if they posed the same threat as a member of a transnational gang.
"These women do not know for certain where their children are, do not know if and when they will be reunited and some have not been able to even speak with them by phone," she said.
Harris alleged that she was allowed to bring phones or cameras inside. "During my visit, I spoke with mothers who have been separated from their children, some as young as five years old," she said, adding that inside the detention centre she spoke with three women from El Salvador and Honduras, who were separated from their children at their border.
"They're in complete and utter despair," she said in her remarks. She said the detainees were being held in a typical prison setting. This is a prison," she said.
Political analysts consider Harris a potential 2020 presidential aspirant. She has earlier slammed Trump for his zero tolerance policy. A day earlier, on the Senate floor, she had urged the Trump Administration to end its zero tolerance policy.
"Let's be clear: a society is judged based on how it treats its children. A society is judged based on how it treats the least among us. And we will be judged harshly. History will judge us harshly because of what this administration has done," Harris said.
"From Trump's Muslim ban to the recent human rights abuses being committed by our government along the southern border, this Administration has been marked by mistreatment of immigrant and refugee communities. We must stand with them no one should be left to fight alone," Harris said in a tweet.