The barrage of gunfire from the 32nd floor of the Mandalay Bay hotel into a crowd of 22,000 people on Sunday night came in extended bursts, sparking panic as music fans cowered on the ground, hemmed in by fellow concertgoers, while others at the edge tried to flee.
More than 525 people were injured – some by gunfire or shrapnel, some trampled – in the pandemonium next to the Las Vegas Strip.
Police said the gunman was Stephen Paddock, 64, who lived in a retirement community in Mesquite, Nevada.
They believed he acted alone and did not know why he attacked the crowd.
Islamic State claimed responsibility for the massacre but the FBI said there was no evidence to link Paddock to any militant organisations.
The preliminary death toll surpassed last year’s massacre of 49 people at a gay nightclub in Orlando, Florida, by a gunman who pledged allegiance to Islamic State.
Police said Paddock had no criminal record.
The gunman killed himself before police entered the hotel room from where he was firing, Clark County Sheriff Joseph Lombardo told reporters.
“We have no idea what his belief system was,” he said.
“I can’t get into the mind of a psychopath.”
Lombardo said 16 firearms were in the room, some with scopes and some that appeared to have been converted to fully automatic weapons.
Police found at least 18 additional firearms, explosives and thousands of rounds of ammunition at Paddock’s home in Mesquite, along with “electronic devices that we are evaluating at this time”, Lombardo told reporters.
Chris Sullivan, the owner of the Guns & Guitars gun shop in Mesquite, said Paddock was a customer who cleared “all necessary background checks and procedures”.
Paddock shared his house with reported Australian girlfriend Marilou Danley, who is in Toyko, Japan.
Authorities want to speak to her upon her return to the US.
The shooting sparked a renewed outcry from some lawmakers about the pervasiveness of guns in the US but was unlikely to prompt action in Congress.
Efforts to pass tougher federal gun laws failed following a number of mass shootings, including the 2012 massacre of 26 children and educators in Newtown, Connecticut, and the June attack on Republican lawmakers practising for a charity baseball game.
“Congress has a moral duty to address this horrific and heartbreaking epidemic,” House of Representatives Minority Leader Nancy Pelosi, a Democrat, said.
The White House said it was too soon to consider gun-control policies.
“Today is a day for consoling the survivors and mourning those we lost,” spokeswoman Sarah Huckabee Sanders said.
“It would be premature for us to discuss policy when we don’t fully know all the facts or what took place last night.”
US President Donald Trump said the massacre “was an act of pure evil” and he would travel to Las Vegas on Wednesday.
The suspected shooter’s brother, Eric Paddock, said the family was stunned by the news.
“We’re horrified. We’re bewildered and our condolences go out to the victims,” Eric Paddock said in a telephone interview, his voice trembling.
Their father had been a bank robber who for a time was listed on the FBI’s 10 most-wanted list of fugitives.
Speaking to reporters from his doorstep in Orlando, Florida, Eric Paddock described his brother as “a wealthy guy” who liked to play video poker and take cruises.