Concertgoers scramble for shelter at the Route 91 country music festival after gunfire breaks out on Sunday in Las Vegas, Nevada. David Becker / Getty Images VIA AFP

BEIJING - President Xi Jinping on Monday sent a condolence message to his US counterpart, Donald Trump, over the mass shooting in Las Vegas in the US state of Nevada.

The shooting caused heavy casualties, Xi said as he extended deep sympathy to the US government and people, profound condolences to the victims, and sincere solicitude to those wounded.

The Chinese president also wished a quick recovery of the injured.

A gunman opened fire on a country music concert in Las Vegas in the US state of Nevada on Sunday night, killing at least 59 people and injuring more than 500 others in the deadliest mass shooting in modern US history, police said on Monday.

More than 22,000 people were attending the outdoor music festival when the gunman rained bullets from a high-floor hotel room of the Mandalay Bay Hotel and Casino on the Las Vegas Strip, the police said.

The Islamic State group claimed responsibility for the attack, saying the shooter had converted to Islam months ago, Reuters reported. The group provided no evidence.

The death toll, which police emphasized was preliminary, would make the attack the deadliest mass shooting in modern US history, eclipsing last year's massacre of 49 people at an Orlando nightclub.

Thousands of panicked people fled, in some cases trampling one another as law enforcement officers scrambled to locate and stop the gunman. Shocked concertgoers, some with blood on their clothes, wandered the streets.

Police identified the gunman as area resident Stephen Paddock, 64, but said they had no immediate information about his motive.