Hundreds of concert-goers fled the scene or ducked for cover amid heavy gunfire. Photo: Getty Images

A gunman, named as 64-year-old Nevada resident Stephen Paddock, opened fire from the 32nd floor of the Mandalay Bay Hotel towards an open-air music festival attended by 22,000.

He was found dead after officers stormed the room where a number of guns were found.

The attack is the worst mass shooting in recent US history.

US President Donald Trump tweeted his "warmest condolences and sympathies" to the victims and their families, and called the shooting "terrible".

Sheriff Joe Lombardo described the shooting as a "lone wolf" attack and there was no information about Paddock's motives.

"We have no idea what his belief system was," he said.

Police say he may have shot himself.

Sheriff Lombardo added that police were now confident they had located a woman, earlier named as Marilou Danley, who was thought to have been travelling with the gunman before the attack.

A police statement said the shooting began at 22:08 local time on Sunday (05:08 GMT on Monday). Paddock was described as a white male from Mesquite, some 60 miles (100 km) north-east of Las Vegas.

'Attack will stun America'

By the BBC's James Cook, in Las Vegas

This has been a mass shooting which has shocked Las Vegas - it has stunned this city. It is very clear that it will be an event which will stun the USA too, a country in which, regrettably, such mass shootings - even if on a lesser scale - are not uncommon.

As to to why the gunman may have carried out this attack, there is no indication of motive at this stage. He was said to have had a large arsenal, a huge number of weapons in that hotel room, which police finally stormed using explosives.

As to why he would have set himself up up there in that way, to do as he did, it is just so, so difficult to fathom.

Witnesses reported that hundreds of shots were fired.

Hundreds of people fled the scene and the sound of what appeared to be prolonged automatic gunfire could be heard on videos posted on social media.

Many hotels on the Las Vegas strip close to the scene remained on police lockdown and parts of Las Vegas Boulevard were shut.