Throngs of people joined rallies across the country Thursday to protest the federal policy of separating children from their parents at the Southern border.

Marches and rallies took place or were planned for later in the day in more than a dozen states, including California, Texas, Michigan and New York, to draw attention to what organizers characterized in a statement as the Trump administration's "cruel and inhumane treatment of immigrants and asylum seekers."

About 60 cities and towns across the country were expected to participate, said Anna Tarkov, communications director for Families Belong Together, a group opposed to the family separations.

Gabriela Domenzain, director of the Latino Policy Institute at Roger Williams University in Bristol, Rhode Island, was among several dozen people who rallied Thursday in nearby Warwick.

Domenzain told NBC affiliate WJAR of Providence that she took part because "putting kids or parents in cages is not something we stand for."

"This is inhumane," she said. "International organizations need to get involved."

Several dozen people marched in Rutherford, New Jersey, where the Rev. Ron Verblaauw, pastor of Rutherford Congregational Church, told NBC New York: "Separating children from families is the first sign we are not the land of the free and the home of the brave anymore. We are the scared."

Micaela Eller, lead organizer of Thursday's rally in Austin, Texas, called the so-called zero tolerance policy cruel, telling NBC affiliate KXAN that the stories from parents are heartbreaking.

"It's hard to look at the images, hear the stories, to listen to the mothers' stories of their children being taken away and just being told, 'We're taking them to give them a bath,' and then never seeing them again," Eller said.

Lydia Ponce, a well-known Los Angeles activist, joined about 200 other people early Thursday evening in the city's historic MacArthur Park.

"It's about humanity," Ponce told NBC Los Angeles. "It's not about left or right. It's not a political thing. It's a humane thing."

About 50 people rallied Thursday morning at Lima Town Square in Lima, Ohio, where Beth Sutton-Ramspeck, an associate professor of English at Ohio State University at Lima, told NBC affiliate WLIO that "you don't do that to a child" and "you don't do that to a parent."

"It's cruel. It's inhumane," Sutton-Ramspeck said. "It's un-American. It's un-Christian. It's wrong."

The rallies come as NBC News was granted access to a facility in Brownsville, Texas, that houses children separated from their parents, as well as minors who came to the United States alone.

Last month,Attorney General Jeff Sessions announced the policy, which seeks to prosecute people who cross the border illegally, a misdemeanor for the first offense. When parents are charged, they end up in federal custody, and their children are separated from them and rendered unaccompanied. Sessions has looked to deter migrants at the border and has said the administration wants to crack down on potential human trafficking and smuggling.

In a speech Thursday to law enforcement officers in Fort Wayne, Indiana, Sessions promised: "If you cross the Southwest border unlawfully, then the Department of Homeland Security will arrest you and the Department of Justice will prosecute you. That is what the law calls for — and that is what we are going to do.

"Having children does not give you immunity from arrest and prosecution," he said.

Tarkov, of Families Belong Together, said in an interview that supporters had flooded the group's in-boxes asking what they can do to challenge the policy.

"The outrage and the desperation is through the roof," she said.

The National Domestic Workers Alliance, an advocacy group, was also supporting the Flag Day rallies.

"The outrage and opposition will only keep growing if the administration continues this cruelty of separating families," Jess Morales Rocketto, political director of the alliance, said in a statement.

Families Belong Together also hosted a virtual event where supporters could sign petitions, get in contact with elected officials and donate to organizations that work to protect children separated from their families.

It's the second wave of major protests against family separations across the country. Activists rallied on June 1 and filed a complaint with the Inter-American Commission on Human Rights, an agency of the Organization of American States, alleging that the U.S. policy violates human rights.