The bidding process has begun in San Diego, California, for contractors competing for the best design for US President Donald Trump’s divisive US-Mexico border wall.

Contractors are submitting their designs ahead of the White House's promised construction of a wall along the US border with Mexico, according to a statement by the US Customs and Border Protection (CBP) Agency.

The contestants will provide border wall prototypes as part of the contest, already dubbed a "beauty pageant," according to the Telegraph. Between four and eight of the best prototypes will make it to the final round of judging, during which companies will have to build sample sections of the wall in 30 days.

"There's a contracting process that has to go on so we're evaluating proposals now. We have to make decisions against that and then we'll have to see what the planning allows for. We think it's summer but I can't be more exact than that… I think that gives us until September," Ron Vitiello, acting deputy commissioner of CBP, said of the proposed timeline.

According to Vitiello, the prototype walls will be constructed "pretty close together."

"There'll probably be more than one or two of them there at the same time but we'll have to sequence it so they're not in each other's way," he said.

San Diego, California's southernmost metropolis, has been chosen for the final stage of the contest because it currently features a section of the border that lacks proper fencing; the border there was breached more than 800 times last year. At the same time, San Diego has "mature" infrastructure and the technology available for the construction process.

"People trying to make their way into the US illegally in the San Diego area may have their choice of eight kinds of border wall to tackle by September," Newser's Rob Quinn wrote.

The best design will be used for hundreds of miles of border wall, a project estimated to cost about $21.6 billion. However, the Department of Homeland Security has managed to secure only $20 million so far, enough to build the prototype samples, the Guardian reported.

Interestingly, the border wall, if it is completed, will not actually span the whole US-Mexico border, as natural borders, such as high mountains, deep canyons and bodies of water provide enough of an obstacle to slow undocumented immigrants down enough for the border guard to handle them effectively, Vitello said.

On the campaign trail ahead of the 2016 presidential election, Trump controversially called Mexican immigrants rapists and said they brought drugs and crime with them across the border. The statements outraged many in the US. He insisted he would stem the flow of migrants by building a wall along the US-Mexican border and force the Mexican government to pay for the construction expenses.