Las Vegas shooting an "act of pure evil": Trump

Trump also called for unity, asserting that in moments of tragedy and horror, America has always stood united.

"Last night, a gunman opened fire in a large crowd at a country music concert in Las Vegas, Nevada. He brutally murdered more than 50 people and wounded hundreds more. It was an act of pure evil," Trump said in his address to the nation from the White House.

As a mark of respect for the victims of the senseless act of violence, Trump issued a proclamation ordering that the US flag be flown at half-staff at the White House and other federal buildings.

Trump said he would be travelling to Las Vegas on Wednesday to meet with law enforcement, first responders and the families of the victims. Trump will travel to Puerto Rico tomorrow.

"Hundreds of our fellow citizens are now mourning the sudden loss of a loved one: a parent, a child, a brother or sister. We cannot fathom their pain. We cannot imagine their loss," Trump said.

"To the families of the victims, we are praying for you, and we are here for you, and we ask God to help see you through this very dark period," he said while consoling his countrymen.

At least 50 people were shot dead and another more than 400 injured when a gunman went on a shooting rampage during a music festival in the casino city of Las Vegas, making it the deadliest mass shooting in the United States.

"Scripture teaches us the Lord is close to the broken-hearted, and saves those who are crushed in spirit. We seek comfort in those words, for we know that God lives in the hearts of those who grieve.

"To the wounded who are now recovering in hospitals, we are praying for your full and speedy recovery, and pledge to you our support from this day forward," Trump said.

The FBI has joined the investigations.

The gunman identified as Steven Paddock, 64, was a local Las Vegas resident, was killed in a 32nd floor of a hotel room. The police have also located an Asian female identified as Marilou Danley, 41, who has been described as roommate of the shooter.

The police said they received first reports of active shooting from a Mandalay Bay Hotel towards a musical concert taking place across the road.

The gunman was shooting from the 32nd floor of the hotel.

He was shot dead later during an exchange of fire with the police.

"We call upon the bonds that unite us: our faith, our family and our shared values; we call upon the bonds of citizenship, the ties of community, and the comfort of our common humanity," he said.

"Our unity cannot be shattered by evil. Our bonds cannot be broken by violence. And though we feel such great anger at the senseless murder of our fellow citizens, it is our love that defines us today, and always will, forever," he said.

Trump said he and the First Lady Melania were praying for every American who has been hurt, wounded or has lost the loved ones in the "terrible" attack.

"We pray for the entire nation to find unity and peace. And we pray for the day when evil is banished, and the innocent are safe from hatred and from fear," he said.

"My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting," Trump had tweeted earlier.