Donald Trump has described Stephen Paddock – who killed 59 people and injured more than 500 in America's deadliest mass killing in modern history – as a “very sick, demented” man.

Multiple government agencies are investigating what led the 64-year-old to open fire from a Las Vegas hotel room into a crowd of some 22,000 concert-goers.

“He’s a sick man, a demented man. A lot of problems, I guess,” Mr Trump told reporters before boarding his Marine One helicopter as he makes his way to hurricane-ravaged Puerto Rico.

“We are looking into him very, very seriously. But we’re dealing with a very, very sick individual,” the President added.

Police said they believed Mr Paddock killed himself before they stormed his hotel room on the 32nd floor of the Mandalay Bay, which is next to the concert site.

The shooting has reignited the controversy over gun ownership laws, but the White House and Republicans have brushed aside attempts to discuss gun policy.

When asked whether the Las Vegas shooting would prompt him to take up gun control legislation, Mr Trump responded: “Look, we have a tragedy. What happened is, in many ways, a miracle.”

Las Vegas shooting – in pictures Show all 15 1 /15 Las Vegas shooting – in pictures Las Vegas shooting – in pictures People scramble for shelter at the Route 91 Harvest country music festival after gun fire was heard Getty Las Vegas shooting – in pictures People carry a person at the Route 91 Harvest country music festival after shots were fired David Becker/Getty Las Vegas shooting – in pictures People run from the Route 91 Harvest country music festival after gun fire was heard David Becker/Getty Las Vegas shooting – in pictures A handout photo released via Twitter by Eiki Hrafnsson (@EirikurH) showing concertgoers running away from the scene (C) after shots range out at the Route 91 Harvest festival on Las Vegas Boulevard EPA/Eiki Hrafnsson Las Vegas shooting – in pictures People lie on the ground at the Route 91 Harvest country music festival after hearing gun fire Getty Las Vegas shooting – in pictures A man in a wheelchair is taken away from the Route 91 Harvest country music festival after hearing gun fire David Becker/Getty Las Vegas shooting – in pictures People stand on the street outside the Mandalay Bay hotel near the scene of the Route 91 Harvest festival on Las Vegas Boulevard EPA/Paul Buck Las Vegas shooting – in pictures FBI agents confer in front of the Tropicana hotel-casino after a mass shooting during a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures Las Vegas police run by a banner on the fence at the Route 91 Harvest country music festival grounds after shots were fired David Becker/Getty Las Vegas shooting – in pictures An injured person is tended to in the intersection of Tropicana Ave. and Las Vegas Boulevard after a mass shooting at a country music festival Ethan Miller/Getty Las Vegas shooting – in pictures Metro Police officers pass by the front of the Tropicana hotel-casino after a mass shooting at a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures A woman sits on a curb at the scene of a shooting outside of a music festival along the Las Vegas Strip AP/John Locher Las Vegas shooting – in pictures A cowboy hat lays in the street after shots were fired near a country music festival in Las Vegas Getty Las Vegas shooting – in pictures Las Vegas Metro Police and medical workers stage in the intersection of Tropicana Avenue and Las Vegas Boulevard South after a mass shooting at a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures Sheriff Joe Lombardo (2-R) speaking during a press briefing in the aftermath of the active shooter incident on Las Vegas Boulevard EPA

“The police department, they’ve done such an incredible job,” he added. “And we’ll be talking about gun laws as time goes on. But I do have to say, how quickly the police department was able to get in was really very much of a miracle. They’ve done an amazing job.”

Police found at least 23 weapons inside Mr Paddock's hotel room, including multiple rifles.

Mr Trump will visit Las Vegas on Wednesday.

Christopher Sullivan, general manager of Guns & Guitars, a gun shop in Mesquite, Nevada, confirmed that Mr Paddock had bought firearms at his store. Mr Paddock never gave any indication that he might have been unstable, Mr Sullivan said in a statement.

The gun shop owner also said Mr Paddock showed no signs of being unfit to buy guns. All the purchases were legal and cleared routine federal screening, Mr Sullivan said.