02/10/2017 16:02 SAST | Updated 02/10/2017 16:03 SAST

Family Of Gunman Behind Worst Mass Shooting in US 'Horrified and Stunned'

“We are completely dumbfounded ... We’re bewildered and our condolences go out to the victims.”

The family of a gunman who killed at least 50 people and injured hundreds more after firing on concertgoers in Las Vegas say they are "horrified" he's behind what is now the worst mass shooting in US history.

Stephen Craig Paddock, 64, opened fire at the final night of the sold-out three-day Route 91 Harvest country music festival near the Mandalay Bay Resort and Casino on the city's strip at about 10.20pm local time on Sunday.

The massacre, undertaken from the 32nd floor of the resort, surpasses that of the Orlando shooting where 49 people were killed.

The suspected shooter's brother, Eric Paddock, said the family was stunned by the news that he was the gunman who unloaded magazines of bullets into the 22,000-strong crowd.

David Becker via Getty Images
Concertgoers duck for cover as gunman Stephen Paddock opens fire from the 32nd floor of the Mandalay Bay Resort and Casino

Police found 10 guns in Paddock's hotel room, which he checked into on September 28.

"We are completely dumbfounded," he said. "We can't understand what happened."

"We have no idea. We're horrified. We're bewildered and our condolences go out to the victims," Eric Paddock said in a brief telephone interview with news agency Reuters, his voice trembling.

"We have no idea in the world."

Police earlier told CBS News that the gunman was white, had been living in a retirement community and hadn't had any run-ins with law enforcement. He wasn't a veteran, Mesquite police added.

"We have no information into his background that is derogatory," Sheriff Joseph Lombardo of Clark County confirmed on Monday afternoon.

Ethan Miller via Getty Images
Police officers point their weapons at a car driving down closed Tropicana Ave near Las Vegas Boulevard after the shooting where 406 people were injured

He said Paddock had been given a citation previously that had been dealt with by "normal procedure through the court system".

Asked if authorities think the shooting was an act of terrorism, Lombardo replied, "No. Not at this point. ... We don't know what his belief system was at this time."

Lombardo, during his latest press conference, refused to call the shooting an act of terrorism, saying they had yet to locate any items that suggested what Paddock's motivations might be.

In the immediate aftermath of the shooting, police were seeking "a companion" of the shooter, named Marilou Danley, who was later identified as being an Australian passport holder, possible of Indonesian decent.

Lombardo said Danely, 62, had since been located and ruled out of the investigation. She was "out of the country", the officer said, and Paddock had been "utilising her ID".

The couple's home in Mesquite is currently being searched.

Lombardo said police did not have an "accurate" picture of the death toll but believe at least 50 people had died and more than 200 injured. Among the dead is an LVMPD officer who was off-duty at the time.

Two other off-duty officers were injured in the shooting. One was initially in a critical condition, but had since improved to stable. The other did not suffer life-threatening injuries.

Four hundred and six people were taken to hospital. Lombardo said during his latest update that number was "well over 400" but could not give accurate numbers as police were still trying to account for everyone that attended the concert.

The death toll increased from 20 to 50 within three hours earlier today and the number of injured doubled.

Police said they believe Paddock, a Las Vegas local, was the "sole aggressor" and acted alone.

It was initially reported that police had shot Paddock dead, but Lombardo has since said Paddock took his own life before police located him.

Lombardo earlier today dismissed reports that there were multiple shooters, incidents at other locations and explosions.

Police had descended on the Ali Baba Restaurant, about a 10-minute drive from the Mandalay Bay, and they also investigated reports of a shooting at the New York-New York Hotel and Casino, not far from the concert ground, amid the chaos of the shooting.

One explosion heard, police said, was the Swat team, entering the Mandalay Hotel to capture Paddock.

The police reported clearing out the Mandalay Bay's 29th floor and working their way up to the 32nd floor.

British Prime Minister Theresa May said the United Kingdom's thoughts were with the victims of what she called an "appalling attack".

British Foreign Secretary Boris Johnson said he was "horrified" by the attack and said the United Kingdom "stands with the American people against this indiscriminate violence".

Johnson added: "My thoughts are with all those caught up in it."

He said the Foreign and Commonwealth Office is in contact with Las Vegas authorities to establish whether any British people were caught up in the attack "and we are ready to help however we can".

British tennis player Laura Robson was caught up in the shooting but escaped unscathed. She described the tragedy as "scary shit".

US President Donald Trump extended: "My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you!"

David Becker via Getty Images
50 people are dead and more than 200 injured after a gunman opened fire on concertgoers in Las Vegas

One witness told ABC news how the gunfire sounded like "fireworks", but after the "second volley" of shot his friend got hit and "people started diving on the ground".

"It [the gun fire] just continued and it was chaotic. Lots of people got hit."

The man said it took "a while" to get his friend, who had three wounds to the chest, to safety. They needed to get him over a fence and spent some time "hiding under the stage to be safe" before finally loading him into a vehicle, only to be "turned around because there was an active shooter".

The witness said he got his friend and some other injured concertgoers into an ambulance, "one guy ended up dying in my arms because he was bleeding so much".

The man's "buddy" survived.

Jason Aldean was said to be performing when the rampage began, but was bundled safely off stage as the chaos ensued.

He later wrote on Instagram that the night had been "beyond horrific".

Kodiak Yazzi, 36, told Associated Press that he and his girlfriend were watching Aldean's performance when he heard what sounded like fireworks.

The 36-year-old said the music stopped temporarily and then resumed before another round of gunfire caused the singer to flee the stage.

Thousands fled as bursts of gunfire could be heard for more than five minutes, Yazzi said.

A Bakersfield police officer was one of the injured.

David Becker via Getty Images
Police guard along the streets outside the the Route 91 Harvest country music festival grounds after a active shooter was reported on Monday

Concertgoers reported flashes from gunfire on the upper floors of the Mandalay Bay hotel across the Las Vegas Boulevard from the festival.

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.

The hotel is near McCarran International Airport, which said on Twitter that it had temporarily halted flights after the shooting. Later, the airport said some flights had resumed.

(Warning: Some readers may find the following footage disturbing.)

David Becker via Getty Images
People run for cover at the Route 91 Harvest country music festival after gunfire erupted
David Becker via Getty Images
Police have confirmed that one suspect had been shot - it is not known if the suspected shooter is wounded or dead
David Becker via Getty Images
A police officer was among those injured