After meeting with some of the victims of the worst mass shooting in modern American history, President Donald Trump said that the shooter was a "very demented person."

"It's a very sick man. He was a very demented person," Trump told reporters as he left the University Medical Center, which has cared for dozens of shooting victims.

Trump said he still doesn't know what motivated Stephen Paddock, 64, to open fire on an outdoor country music festival on the Las Vegas Strip late Sunday night, but "we're looking very hard" for answers. At least 59 people were killed in the attack and more than 500 were injured.

Throughout his four-hour visit to Las Vegas on Wednesday afternoon, Trump repeatedly praised police, first responders and average Americans who quickly worked to save the lives of others on Sunday.

Advertisement

"In the depths of horror, we will always find hope in the men and women who risk their lives for ours," Trump said during a brief speech at the end of his visit.

"The mass murder that took place on Sunday night fills America's heart with grief. America is truly a nation in mourning."

At the hospital, Trump said that this was his message to the patients that he met: "We're with you 100 per cent."

And the president said that he invited many of those he met to come visit the White House.

"I said, 'If you're ever in Washington, come on over to the Oval Office.' And they're all saying, 'We want to do it. How do we do it?'" Trump said.

"And, believe me, I'll be there for 'em. But the message that I have is that we have a great country, and we are there for you, and they're there for us."

When a reporter asked the president about gun violence, he responded: 'We're not going to talk about that today."

Trump also visited the Las Vegas Metropolitan Police Department, where he gave a brief speech and met with law enforcement officers and other first responders who were called into action on Sunday night.

"I was a fan before this - you know that, everyone in this room knows that, a big fan before this. And, I guess, if you can be more of a fan, I guess I'm even more of a fan now,"
Trump told the officers.

"But you showed the world and the world is watching and you showed what professionalism is all about. Because that was fast. Something like that could take place for hours and hours and hours and you can't figure it out, and you should be very proud."

As Trump toured a command center, he told those in uniform: "You are a real inspiration. This is a rough time but if you didn't get up there so quickly, it could have been worse - it could have been a lot worse."