Photo: The Canadian Press

Protesters hold up signs during a rally against a visit by President Donald Trump in Beverly Hills, Calif. 

President Donald Trump on Tuesday eagerly inspected eight towering prototypes for his long-sought wall at the U.S.-Mexico border and accused California of putting "the entire nation at risk" by refusing to take tough action against illegal immigration.

Trump, making his first trip to California as president, said he preferred a fully concrete wall because it was the hardest to climb, but he noted that it needed to be see-through. He said the first thing he noticed on the drive to the border was the patched-up holes in part of the existing fence.

"We have a lousy wall over here now, but at least it stops 90, 95 per cent," Trump said. "When we put up the real wall, we're going to stop 99 per cent. Maybe more than that."

Trump's visit was greeted with peaceful protests by demonstrators both for and against his planned wall. The trip came amid an escalating battle between his administration and the liberal state, which has refused to help federal agents detain immigrants in the U.S. illegally.

The president renewed his criticism of Democratic Gov. Jerry Brown, saying Tuesday that he was presiding over sky-high tax rates and that the state's sanctuary policies "put the entire nation at risk."

"They're the best friend of the criminal," Trump said. "That's what exactly is happening. The criminals take refuge in these sanctuary cities and it's very dangerous for our police and enforcement folks."

The Justice Department last week sued to block a trio of California laws designed to protect people living in the U.S. illegally. Brown accused U.S. Attorney General Jeff Sessions of "going to war" with California to appease Trump.

After leaving the border, Trump basked in the cheers of U.S. Marines in Miramar, pointing to his work to build up the nation's military. He also suggested there may someday be a "space force" fighting alongside the nation's military branches.

A few hundred protesters for and against Trump faced off at a Beverly Hills park. A group of pro-immigration demonstrators chanted, "Say it now, say it clear, immigrants are welcome here."