El Paso native and presidential candidate Beto O’Rourke accused Mr Trump of being a “white nationalist” whose rhetoric is “encouraging violence and racism” as he responded to the Saturday shooting at a Walmart store in El Paso, Texas.

The city is close to the US-Mexico border, in the region which has been the focus of some of Mr Trump’s most hate-filled and divisive remarks.

Fellow presidential candidate Bernie Sanders responded to reports of the gunman’s “racist” manifesto by calling on supporters to also “reject this dangerous and growing culture of bigotry espoused by Trump and his allies.”

He condemned the US policy of “wasting money putting children in cages” and called for more resources to counter “the scourge of violent bigotry and domestic terrorism” that has gained momentum under Donald Trump’s administration.

Nine people were killed and at least 26 injured in a mass shooting in Dayton, Ohio, just hours after the Texas attack, though police had not announced a suspect’s name or motive before the Star went to press.

A 21-year-old white man arrested at the scene in El Paso reportedly posted a document just before the attack claiming that the violence was a response to “the Hispanic invasion of Texas.”

The suspect has been named by US media as Patrick Crusius. A Twitter account under his name shows support for Mr Trump, including on his policy to build a border wall between the US and Mexico.

El Paso Police Chief Greg Allen said the four-page document, posted on the notorious forum site 8chan, pointed to a “potential nexus to a hate crime.” The website is frequently used by the far right and white supremacists due to its lax moderation policy.

The document appeared online 20 minutes before the gunman opened fire. It expressed support for the New Zealand mosque attacker who shot dead 51 people in Christchurch in March and had also been a user of the 8chan site.

Speaking on CNN, Mr O’Rourke warned that Mr Trump’s intolerant speech was “reminiscent of something you might hear in the Third Reich.”

He said: “Let’s be very clear about what is causing this and who the president is. He is an open avowed racist and is encouraging more racism in this country.”

Republican Texas Governor Greg Abbott said: “We’re going to aggressively prosecute it both as capital murder but also as a hate crime, which is exactly what it appears to be.”

In a damning indictment of US policy towards migrants, authorities said that many of those injured may not seek medical help over fears they may be deported due to their immigration status.

Juliette Kayyem, a former assistant secretary at the US Department of Homeland Security, told CNN that victims being deterred from hospitals was “a concern.”

She said: “It’s clear there’s people who are not unifying with their family, and that there are people they’re worried are injured that did not go to hospitals, likely because of their immigration status.”

The Hope Border Institute, a faith-based group offering support to those on the US-Mexican border, urged undocumented victims to contact them for help. (IPA Service)