The President was accompanied by First Lady Melania Trump on his visit to the Nevada city.
As well as meeting some of those who survived the attack, they spoke to first responders and doctors treating the hundreds of people who were wounded.
He praised the “professionalism” of hospital staff who worked to save victims of Sunday night’s atrocity – saying they did an “indescribable” job.
At least 59 people were killed and more than 500 injured when Stephen Paddock targeted a crowd of 22,000 people attending a country music festival.
The President said: “I just met some of the most amazing people. We met patients who were absolutely, terribly wounded, and doctors and nurses who have done a job that’s indescribable.”
He added: “What I saw today was an incredible tribute to professionalism and what they have done is incredible. You never want to see it again.”
And then he highlighted the “bravery” of patients.
He said: “Some were very, very badly wounded, and they were badly wounded because they refused to leave and wanted to help others because they saw people going down all over.
“It’s an incredible thing to see. Tremendous bravery.”
Mr and Mrs Trump spent 90 minutes meeting privately with victims and their families, and the President revealed he had invited several of them to visit the White House in Washington.
Standing alongside doctors at the University Medical Centre, he said: “It makes you very proud to be an American when you see the job they’ve done.
“I just want to congratulate everybody. It’s incredible. The message that I have is that we are a great country. We are there for you.”
Mr Trump deflected a reporter’s question about whether the US has a problem with gun violence, telling them: “We’re not going to talk about that today.”
On a sombre note, he added: “Our souls are stricken with grief for every American who lost a husband or a wife, a mother or a father, a son or a daughter. We know that your sorrow feels endless.
“We stand together to help you carry your pain. You are not alone. We will never leave your side.”
Mr Trump then headed to the Las Vegas Metropolitan Police headquarters, where he met police officers and dispatchers who had responded to the shooting.
He congratulated them “on a job well done”.
“You showed the world and the world is watching,” he told them. “And you showed what professionalism is all about.”
Meanwhile, so-called “comfort” dogs are being used in Las Vegas to help those affected by the mass shooting.
The therapy canines have been seen in a number of medical centres as well as the Las Vegas Convention Center where families of some of the victims waited for news on their loved ones.