U.S. Homeland Security Secretary Kristi Noem said Tuesday that the entire border wall along the southern border with Mexico is going to be painted black — a move she credited to U.S. President Donald Trump — to make it hotter and deter illegal immigration.

Noem spoke during a visit to a portion of the wall in New Mexico, where she also picked up a paint roller to help out with the painting.

She touted the wall's height and depth as ways to deter people seeking to go over or under it. And then Noem said Homeland Security was going to be trying black paint to make the metal hotter.

"That is specifically at the request of the president, who understands that in the hot temperatures down here when something is painted black it gets even warmer and it will make it even harder for people to climb. So we are going to be painting the entire southern border wall black to make sure that we encourage individuals to not come into our country illegally," Noem said.

U.S. Border Patrol Chief Mike Banks, who attended the event with Noem, said the paint would also help deter rust.

Billions for Homeland Security

During Trump's first term, building the wall was a central focus of his hardline immigration policy. During his second term, his mass deportation agenda with arrests in the interior of the country has been the main focus, but Homeland Security will be getting about $46 billion US to complete the wall as part of new funding passed by Congress this summer.

Noem said they have been building hundreds of metres of barrier every day.

"The border wall will look very different based on the topography and the geography of where it is built," she said.

She said that in addition to barriers like the one she visited Tuesday, the department is also working on "water-borne infrastructure." Long sections of the border between the U.S. and Mexico sit along the Rio Grande River in Texas.

The Trump administration is pushing forward with completing the wall at the same time that the number of people crossing the border illegally has plummeted.