The US government has begun erecting tents close to the border with Mexico to house detained migrants – even as Donald Trump likened the influx of undocumented families entering the US to “Disneyland” on Sunday.

Life at the foothills of the Franklin mountains in El Paso, Texas has been rudely disrupted in the last few days by construction crews coming and going near the adjacent border patrol station.

The main frames of two large tents popped up last week. They are expected to hold up to 500 migrants amid a level of chaos at the border that has unfolded under the Trump administration’s immigration policies.

Construction crews are now working to prepare the interior of the shelter, which is expected to be operational by 1 May, even as the president downplayed conditions in which migrants are held and appeared once again to support the separation of families crossing the border.

He told the Fox News show Sunday Morning Futures: “When they used to separate children, which was done during the Obama administration, with Bush, with us, with everybody [see footnote], far fewer people would come, and we’ve been on a humane basis, it’s pretty bad.”

He added to the host, Maria Bartiromo: “We go out and we stop the separation. The problem is you have 10 times more people coming up with their families, it’s like Disneyland now.”

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As the continuing arrival of migrants to the southern border has put a strain on processing capacity at US Customs and Border Protection (CBP) facilities, finding space to house the rising number of migrants in the immediate aftermath of their undocumented crossing into the US has become one of the biggest challenges for immigration officials and non-governmental organizations.

The Trump administration began separating thousands of migrant families last year whenever they crossed the US-Mexico border unlawfully, and detaining parents and children separately, under a “zero-tolerance” policy. Trump halted the policy last summer after widespread uproar, though in recent weeks, even as the government is being sued over the consequences, floated, then rejected again, the idea of resuming such actions.

CBP said in a statement last week that the large number of arrivals had created a need to open up additional shelter space in order to continue to process migrants arriving at the border.

“The humanitarian and border security crisis on our south-west border has stretched our resources and processing facilities to the breaking point,” said John Sanders, the senior official performing the duties of commissioner. “These temporary facilities will support our efforts to process, care for and transfer the unprecedented number of families and unaccompanied children crossing the border each day.”

Last month, CBP was criticised by local advocates and public officials after it chose to house hundreds of migrants in open-air conditions underneath the Bridge of the Americas that crosses the border between El Paso and its Mexican sister city, Juárez. The pen where migrants were being held closed a few days after the press began to report the harsh conditions of the improvised shelter.

In a press conference held at the end of March, El Paso’s Democratic congresswoman, Veronica Escobar, urged CBP to consider putting in place such emergency shelters to hold migrants instead of keeping them fenced in under the bridge. She sharply criticised the government’s handling of migration at the border, calling CBP’s handling of migrants a crisis of leadership.

Other prominent critics of the president have accused the administration of “manufacturing” a crisis at the border for its own anti-immigration purposes, while creating genuine chaos in the process.

On 19 April CBP awarded a contract to Deployed Resources LLC of Rome, New York, for the construction of the two temporary facilities being built in El Paso, at the western end of the Texas-Mexico border and Donna, near McAllen, in eastern Texas. The total cost for the construction is valued at $36.9m for a four-month period. CBP has four one-month extension options if deemed necessary, the agency said.

Although the new temporary facilities are a step above being made to sleep rough under a bridge, as the temperatures in El Paso are beginning to reach the high 80s, some local advocates have concerns about the treatment that the migrants may face inside the new encampments.

The sight of the tents going up in El Paso is a throwback to just a few months ago when the government was detaining child migrants in an encampment at nearby Tornillo.

The camp started small last summer and was meant to exist for just weeks, but ended up expanding fivefold and enduring for months, amid protests and local opposition, until it was closed in January.

Facebook Twitter Pinterest The new migrant shelter lies at the foothills of the Franklin Mountains. Photograph: Edwin Delgado/The Guardian

Dylan Corbett, executive director of the immigration advocacy group Hope Border Institute in El Paso, said that he had heard multiple allegations of verbal and physical abuse migrants endured while detained under the bridge.

“The federal government has waited too long and this is not a solution, but unfortunately it might be necessary to accommodate everyone that’s coming. We have to make sure this is not a place where human rights are violated, as we’ve seen that in these makeshift facilities,” Corbett said. He called the tents “a Band-Aid solution”.

Shaw Drake, a policy counsel for the ACLU border rights center in El Paso, said the main concern was how migrants are treated inside the shelters. Both advocates are appealing for more transparency, accountability and government oversight as the number of migrants in detention continues to rise.

“It’s possible to have humane conditions for the migrants being detained in these tents, the issue is that border patrol has an extensive history of abusive conditions in its facilities and there is no indication that would not continue to occur,” Drake said.

Multiple requests for comment made to CBP were not addressed.

Although the new facilities are expected to be fully equipped to act as shelters, Corbett questions yet another expansion of detention space for immigration processing and is worried it may set the stage for future policies that exacerbate the humanitarian crisis at the border.

“The federal government is fully on board in pursuing a policy where it would like to detain everyone that comes to the border and we believe that is simply unjust,” he said. “We don’t believe that anyone should be detained if they aren’t a threat to the security of our communities.”

• This footnote was added on 2 May 2019. Contrary to Donald Trump’s assertion, the Obama administration had no blanket policy of separating families.