WASHINGTON - US President Donald Trump on Monday described the mass shooting at a Las Vegas music festival as "an act of pure evil".

Trump made the televised address to the nation after a gunman killed more than 50 people and wounded hundreds more when he opened fire on a country music concert in Las Vegas on Sunday.

"Last night a gunman opened fire on a large crowd at a country music concert in Las Vegas, Nevada. He brutally murdered more than 50 people and was an act of pure evil," he said.