US President Barack Obama on Tuesday hammered home his belief that Republican White House hopeful Donald Trump would not be elected, saying the job was not like hosting a reality show.

Obama slammed Trump's proposal to ban Muslims from entering the United States, and said his rivals were making similar "troubling" statements. But he reserved his toughest remarks for the billionaire real estate tycoon.

"I continue to believe that Mr Trump will not be president. And the reason is because I have a lot of faith in the American people. And I think they recognize that being president is a serious job," he said.

"It's not hosting a talk show or a reality show. It's not promotion. It's not marketing. It's hard."