WASHINGTON - US President Donald Trump denounced the Las Vegas shooting, which killed at least 50 people and injured hundreds, as an act of pure evil but called for Americans to find "unity and peace", in an address to the nation Monday (Oct 2) after the most deadly mass shooting in modern US history.

A gunman killed 50 concert-goers and wounded around 400 more when he poured automatic fire down on an outdoor Las Vegas venue late on Sunday night.

"Our unity cannot be shattered by evil. Our bond cannot be broken by violence," Trump said in a live address delivered from the Diplomatic Room of the White House at 10:50 am (10:50pm Singapore time), in what has become a grim rite of passage for modern US presidents.

He said he will visit Las Vegas on Wednesday, and that US flags will be flown at half-mast.

The president will be tasked with uniting a nation which is already angrily rehashing stridently held views on the vexed question of gun control.

Hillary Clinton, Trump's Democratic Party rival in last year's election, swiftly called for gun control measures in the hours after the shooting.

She called out the National Rifle Association (NRA) for backing legislation that would make it easier for Americans to purchase gun silencers.

'Our grief isn't enough. We can and must put politics aside, stand up to the NRA, and work together to try to stop this from happening again,' the former Democratic nominee for president said.

Through a series of national crises Trump has sometimes struggled make his empathy felt. Earlier on Monday he offered "warmest condolences and sympathies" to the victims in a tweet.

The issue of gun control is highly sensitive in the United States and Trump's views on the issue have changed markedly over his years in public life.