Disturbing descriptions of the conditions in detention facilities along the Southwest border reverberated throughout the U.S. Tuesday, sparking protests in San Francisco and beyond, and prompting release of a government inspection that revealed shortcomings in the country’s immigration detention system.

At the center of the chaos are accounts from attorneys and doctors who interviewed dozens of migrant children detained at facilities across the border, where they found living conditions that are putting many children at risk of harm or death, they said. At least six children have died in Customs and Border Protection custody since last year.

Their findings painted a dark picture of conditions inside U.S. detention facilities — places rarely seen or accessed by the public — that sent shock waves across the country, spurring politicians to visit the facilities this week and nationwide protests calling on the government to close the camps.

In downtown San Francisco on Tuesday, hundreds of protesters calling for an end to the detention of children at the border closed down a busy intersection at Post Street for about an hour, snarling daytime traffic.

About 400 protesters packed the intersection in front of Sen. Dianne Feinstein’s office at 1 Post St. in San Francisco Tuesday, calling on the government to shut down detention facilities holding children. The crowd blocked traffic for about one hour — stalling public transit — before marching to House Speaker Nancy Pelosi’s office at 7th and Mission streets.

Oher protests were planned in Walnut Creek, Santa Rosa, Las Vegas, El Paso, Chicago, Atlanta and hundreds of other cities.

After details of the conditions were reported, the acting head of CBP, John Sanders, resigned, and President Trump tapped Mark Morgan, former head of Immigration and Customs Enforcement, to take over.

The Department of Homeland Security’s Office of Inspector General on Tuesday released a report further detailing the dire conditions at these border facilities, warning immigration authorities of the potential consequences. During visits to border facilities and two ports of entry, inspectors found severe overcrowding — including standing room only in some facilities — no access to showers, and prolonged detention, the report said.

Bill Hing, director of the Deportation Defense Clinic at the University of San Francisco, can’t shake an image from his head from inside a detention facility in Clint, Texas, recently, where a teenage girl comforted a crying 7-year-old and a toddler.

The teen wasn’t related to the two children. But in this cramped facility where more than 100 minors remain in the custody of U.S. Customs and Border Protection, far away from parents and relatives, she had become their source of comfort.

“I really am constantly thinking about it,” said Hing, a longtime social justice advocate. “I’m really concerned with several of the kids.”

Though Hing and other attorneys have gone inside the detention centers to interview children annually for several years, the conditions they found in this latest inspection were so grim that it spurred them to break protocol and report their findings to the Associated Press and other news media, they said.

CBP has challenged claims that the facilities are unsanitary and dangerous, saying agents are responding in the best and quickest way possible to an overwhelming border crisis that has stretched their resources extremely thin.

“CBP continues to utilize all available resources to prioritize and care for children in our custody and facilitate their expeditious transfer to Health and Human Services,” said an agency spokesman.

By law, a child who enters the U.S. without a parent or legal guardian is considered “unaccompanied” and is transferred to the custody of Health and Human Services. Border agents cannot keep children with a relative, such as a grandparent or aunt and uncle, which is why hundreds of children are sent to Border Patrol facilities for processing.

Children cannot be detained for more than 72 hours but many attorneys and advocacy groups said they’re being detained for days or even weeks.

All of the children interviewed at the Clint facility were detained at the border after presenting themselves to CBP agents with a relative or older sibling, according to Hing. In one case, a 5-year-old boy was separated from his father because the man had a previous criminal conviction, he said.

“This is the worst because it involves children and infants and toddlers,” said Hing. “These are kids on their own, without their mothers and fathers. You just want to hug them. We were told not to. But we did.”

Attorneys reported seeing a lack of hygiene and access to food, sickness and overcrowding, including children with soiled diapers and others who hadn’t showered in several days, mothers wearing shirts stained with breast milk, children sleeping on mats on the floor, and children as young as 8 years old caring for toddlers.

The Center for Human Rights and Constitutional Law last week filed an emergency request in federal district court requesting a temporary restraining order and a contempt order against CBP, demanding that the agency immediately start processing children for release to parents and relatives. It also asked that CBP provide children with necessities while in detention, including adequate food, clean water, medical care, and facilities for sleep.

A CBP spokesman declined to comment on the court filing. There were 117 children at Clint as of June 26, he said.

Attorneys are authorized to inspect detention facilities annually as part of the 1997 Flores agreement, which governs how immigrant children should be cared for while in U.S custody.

Hing, who has conducted previous inspections, during the week of June 17 traveled to Clint, Texas, a farming town about 25 miles south of El Paso, to inspect the detention facility that at one point held an estimated 350 minors. He was joined by about eight lawyers and physicians, including some from the Bay Area.

“They were visibly dirty and very tired and many of them very much seemed to be traumatized,” said Clara Long, a senior researcher at Humans Rights Watch in San Francisco. Long has helped inspect detention facilities for about three years.

“(The visits) always leave me emotionally raw,” she said. “This one was particularly so because of the immediate fear for the children’s safety in those facilities.”

The group was not allowed to go inside the cells or other parts of the facility and was confined to a conference room for interviews, Hing said. Guards prohibited them from taking photos.

Hing interviewed about 20 children in Spanish, some of whom were siblings.

Many kids had the flu, according to Hing. Two infants were so sick that they were rushed to the hospital for emergency care. Everyone received the same meals daily: oatmeal for breakfast, instant noodles for lunch and frozen burritos for dinner. Some children told Hing that they were allowed to go outside and play daily for about 30 minutes.

The children’s declarations have been submitted to the court. Hing and his colleagues have returned to their normal routines but squeeze in phone calls throughout the day to try to track some of the kids they interviewed in hopes of reuniting them with their parents.

Tatiana Sanchez is a San Francisco Chronicle staff writer. Email: tatiana.sanchez@sfchronicle.com. Twitter: @tatianaysanchez.