At least 50 people have died and more than 400 people were injured in the worst ever mass shooting in modern US history at an outdoor concert in Las Vegas.

The gunman, 64-year-old Stephen Craig Paddock, of Mesquite, Nevada, was found dead in a room in the Mandalay Bay Hotel and Casino on Las Vegas Strip with as many as 10 firearms.

SWAT officers who stormed the gunman’s room found that he had killed himself.

A total of 406 people were taken to hospital after the shots were fired on concert-goers at the Route 91 Harvest Festival.

There was no immediate word on the motive for the attack. The US Homeland Security Department said there was no “specific credible threat” involving other public venues in America.

On Twitter, Prime Minister Theresa May wrote: “The UK’s thoughts are with the victims and the emergency services responding to the appalling attack in Las Vegas.”

Foreign Secretary Boris Johnson said he was “horrified” by the attack, and that his thoughts were with those caught up in it.

The Foreign Office said it was in contact with authorities in Las Vegas and that it was “ready to help” any British people affected.

A spokeswoman said: “Our sympathies are with all those affected by the horrific shooting in Las Vegas.

(PA Graphics)(PA Graphics)

“Details about the incident are still emerging and we are in contact with Las Vegas emergency services. We are ready to help any British people affected.

“Any British people in Las Vegas should follow the advice of emergency services, and check the Foreign Office travel advice.”

Country music star Jason Aldean was performing on Sunday night at the end of the three-day festival in front of a crowd of 22,000 when the gunman opened fire from the 32nd floor of the Mandalay Bay Hotel and Casino.

People run during an mass shooting on the Las Vegas Strip (Chase Stevens/Las Vegas Review-Journal via AP)People run during the mass shooting (Chase Stevens/Las Vegas Review-Journal via AP)

Aldean was in the middle of a song when the shooting began. Video of the incident then showed Aldean stopping his performance and the crowd becoming quiet.

The gunman then fired another volley, the muzzle flashes visible from the casino, as more victims fell to the ground, while others fled in panic. Some hid behind concession stands, while others crawled under parked cars.

British tennis star Laura Robson was among those attending the concert.

Map locates shooting in Las Vegas(PA graphic)

She shared two pictures of herself at the event, wearing a cowboy hat with an American flag emblazoned on it.

Asked by a Twitter follower if she was all right, she wrote: “I’m okay. We were right there … sounded like fireworks at first then everyone started running.”

She added it had been a “scary” experience.

A <a href=police officer takes cover behind a police vehicle during a shooting near the Mandalay Bay resort and casino on the Las Vegas Strip (John Locher/AP)">A police officer takes cover behind a vehicle (John Locher/AP)

Witness Kodiak Yazzie, 36, said the music stopped temporarily when the first shots began. After the song started up again, the second round of pops sent the performers ducking for cover and fleeing the stage.

“It was the craziest stuff I’ve ever seen in my entire life,” Mr Yazzie said. “You could hear that the noise was coming from west of us, from Mandalay Bay. You could see a flash- flash- flash- flash.”

Monique Dumas from British Columbia, Canada, said she was at the concert, six rows from the stage, when she thought she heard a bottle breaking, and then a burst of popping sounds that may have been fireworks.

Mandalay BayDrapes billow out of broken windows at the Mandalay Bay resort and casino (John Locher/AP)

She said it had been “organised chaos” as everyone fled.

“It took four to five minutes and all that time there was gunfire.”

In addition to Paddock, police said they located a woman who may have been his room-mate – Marilou Danley, 62.

Clark County Sheriff Joseph Lombardo said officers believe this was a “lone wolf” attack.

LockdownLas Vegas police sweep through a convention center area during a lockdown (Chase Stevens/Las Vegas Review-Journal via AP

Police shut down the usually busy Las Vegas Boulevard and authorities across the state and federal ranks converged on the scene as dozens of ambulances ferried those struck by gunfire.

Nearby Interstate 15 and flights at McCarran International Airport were briefly closed.

Hospital emergency rooms were jammed with victims delivered by ambulance. Others loaded the wounded into their cars and drove them to hospitals.

Among those killed were two off-duty police officers who were attending the concert. Two on-duty officers were wounded, including one who underwent surgery and was upgraded to stable condition, police said.

Hours after the shooting, Aldean posted on Instagram that he and his crew were safe and that the shooting was “beyond horrific”.

“It hurts my heart that this would happen to anyone who was just coming out to enjoy what should have been a fun night,” Aldean said.

 

A post shared by Jason Aldean (@jasonaldean) on Oct 2, 2017 at 1:17am PDT

US president Donald Trump tweeted: “My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you!”

Before Sunday, the deadliest mass shooting in modern US history took place in June 2016, when a gunman opened fire at a gay nightclub in Orlando, Florida, killing 49 people.

The brother of the gunman said he is “completely dumbfounded” by the carnage.

In a brief interview with the Orlando Sentinel, Eric Paddock said he cannot understand what happened.

The Pope called the shooting a “senseless tragedy” and said he would pray for victims.

The Vatican secretary of state sent a telegram of condolence to the bishop of Las Vegas, saying Francis was “deeply saddened” to learn of the shooting.

The telegram said the Pope praised the efforts of police and emergency crews.

Las Vegas police said they have determined that the woman thought to have been the gunman’s room-mate is no longer considered a “person of interest” in the inquiry.

Marilou DanleyMarilou Danley is no longer thought to have been involved (Las Vegas Metropolitan Police Department/AP)

Officers do not believe 62-year-old Marilou Danley was involved in the shooting.

Meanwhile, heavily armed police are searching the Nevada retirement-community home of Paddock.

Mesquite Police chief Troy Tanner said officers entered the property where the 64-year-old lived.

He said Ms Danley was not at the house and police saw “no movement” inside the one-storey, three-bedroom home in the Sun City Mesquite retirement community, about 80 miles north of Las Vegas.

Mr Tanner said detectives are at the scene in the resort community, located near the Arizona state line.