Construction is underway on prototypes for Donald Trump’s promised wall along the Mexican border.
Footage and images have started to emerge of the construction of the rival walls near San Diego, California.
The US President has said he will pick the winning design of the four prototypes in a month.
The companies were chosen to build 30ft x 30ft concrete mock-ups of the wall, the country's Customs and Border Protection (CBP) said.
Tests for resistance to tampering and penetration using small tools will then be carried out on the models, a spokesman told the BBC.
The four $500,000 (£387,000) contracts were offered in a bid to help Trump’s government “refine the design standards” of the border wall, CBP deputy commissioner Ronald Vitiello said.
The plans sparked controversy, which was added to when the US leader during his election bid insisted Mexico would pay for the wall.
President Enrique Pena Nieto tweeted at the time: "At the beginning of the conversation with Donald Trump, I made clear that Mexico would not pay for the wall."
The president later backed down and accepted the US would be forced to foot the bill.
Protesters marched across the US and Europe against Trump’s anti-immigration plans, including constructing the divide shortly after he was elected and again 100 days into his term.