The massacre started around 10:08 p.m. Sunday (1:08 a.m. ET Monday) at the Route 91 Harvest festival in las Vegas.

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. He said there was no information about Paddock's motives.

Police don't believe there are any more shooters. "Right now, we believe it's a sole actor, a lone-wolf-type actor," the sheriff said.

Gunman, named as 64-year-old local 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. "We have no idea what his belief system was," he said.

He 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.

Sheriff Lombardo said he was unable to give accurate details of dead and wounded, but confirmed two off-duty police officers were among those killed.

Inputs CNN