Pence traveled to the Mexico border as protesters rallied in several US cities urging the government to shut down what they call "concentration camps."

The vice president visited the McAllen Border Station, where he was taken to a sweltering outdoor portal where 384 men were held in a caged area.

The stench was horrendous, according to media reports from journalists traveling with Pence who were allowed into the area for 90 seconds.

The men, who allegedly crossed the border illegally, were crammed into a space where there was not enough room for all of them to lie down on the concrete floor.

They had no cots, mats or pillows, only silver polyester blankets. Grasping the chain link fencing, they shouted to reporters that they had been there 40 days or longer, were hungry and wanted to brush their teeth.

"To be honest with you, I was not surprised by what I saw," Pence said afterward. "I knew we would see a system that is overcrowded. It's overwhelmed and that's why Congress has to act."

He has blamed Democrats for precipitating the crisis by resisting President Donald Trump's push for border funding, as opposition lawmakers split with the administration over how the money should be spent.

Democrats ultimately bowed to pressure last month as Congress approved $4.6 billion in emergency aid to ease the swelling crisis that has seen an influx of migrants flood into the United States, mostly from impoverished Central American countries.

"What's witnessed here today, and the overcrowding of this border station, and the overall crisis at our border, is that Congress must do more," Pence said.

"(This is) a crisis that is overwhelming our system."

Michael Banks, the patrol agent in charge of the McAllen facility, disputed the detainees' account of the conditions, saying they are allowed to brush their teeth once a day, and that the no one had been held there longer than 32 days.

He said they were given three hot meals a day from local restaurants, as well as juice and crackers.

Banks conceded that many of the men had not showered in 10 or 20 days but that the facility had added a trailer shower on Thursday.

Pence earlier visited a two-month-old migrant processing facility in nearby Donna, a series of large white tents holding 800 people with capacity for 1,000.

He spoke with parents and children there who told the vice president they were well taken care of. Reporters saw stacks of clothes, water bottles, juice and diapers in the facility.

"Every family I spoke to said they were being well cared for," Pence said, decrying the "harsh rhetoric" of Democrats.

- 'Concentration camps' -

Earlier Friday in Washington, the House Oversight Committee held a hearing on migrant children who were separated from their parents.

A Trump administration "zero tolerance" policy launched in 2018 saw more than 2,300 children separated from their parents at the border, before the government backed down.

According to a report published by the committee, at least 18 children under the age of two were separated from their parents for periods ranging from 20 days to half a year.

"The administration is causing problems at the border, not resolving them," committee chairman Elijah Cummings said.

Elora Mukherjee, an academic from Columbia University who visited a center in Clint, Texas, told the commission that some children were still wearing the same clothes that they were in when they crossed the border, and were covered in mucus, saliva and other fluids.

"Because of the smell, it was difficult for me to sit by them," she said.

Protests took place around the country Friday calling for the closure of the detention facilities.

"These are concentration camps. The definition of concentration camp is holding people who are not criminals for racist or ethnic reasons. That is what's happening right now," said Mimi Rosicky, 56, who was among 2,000 people who gathered in San Diego.

Demonstrators outside the White House held up signs with messages like "Uncage Kids" and "I was a stranger and you welcomed me."

"My family came as refugees because they are Jews. It is very important to me that people still be able to come to this country as refugees," Cassie Good told AFP.