A retiree armed with multiple assault rifles strafed an outdoor country music festival in Las Vegas from a high-rise hotel window on Sunday, slaughtering at least 59 people before killing himself in the deadliest mass shooting in modern US history, according to Reuters.

The barrage of gunfire from the 32nd floor of the Mandalay Bay hotel into a crowd of 22,000 people came in extended bursts that lasted several minutes, as throngs of terrified music fans cowered desperately on the open ground, hemmed in by fellow concert-goers, while others at the edge tried to flee.

More than 525 people were injured - some by gunfire or shrapnel, some trampled - in the pandemonium adjacent to the Las Vegas Strip as police scrambled to locate the assailant.

Police identified the gunman as Stephen Paddock, 64, who lived in a retirement community in Mesquite, Nevada. Authorities said they believed he acted alone, although his motive was unknown.

The Islamic State militant group claimed responsibility for the massacre, but US officials said there was no evidence to support the claim.

At least a dozen people were in critical condition at University Medical Center in Las Vegas, where the most seriously injured victims were taken, a spokeswoman said.

The preliminary death toll, which officials said could rise, surpassed last year’s record massacre of 49 people at a gay nightclub in Orlando, Florida, by a gunman who pledged allegiance to Islamic State.

The dead in Las Vegas included a nurse, a government employee and an off-duty police officer.

Shocked survivors, some with blood on their clothing, wandered streets after the shooting, where the flashing lights of the city’s gaudy casinos blended with those of emergency vehicles.

Police said Paddock had no criminal record. The gunman shot and wounded a hotel security officer in the leg through the door of his suite then killed himself before police entered the room, authorities said.

“We have no idea what his belief system was,” Clark County Sheriff Joseph Lombardo said “I can’t get into the mind of a psychopath.”

Federal officials said there was no evidence to link Paddock to militant organisations.