Donald Trump offered his condolences Monday morning to the victims of a mass shooting in Las Vegas that has left at least 50 people dead and more than 400 people injured. It is the deadliest mass shooting in U.S. history.

According to police, 64-year-old Stephen Paddock opened fire on attendees of the Route 91 Harvest Music Festival near the Mandalay Bay Hotel and Casino in Las Vegas on Sunday evening. The scene was described by witnesses as “pandemonium,” with concertgoers rushing for cover.

“My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting,” Trump wrote on Twitter. “God bless you!”

Vice President Mike Pence also took to Twitter to thank first responders for their courage. He added: “To victims, families & loved ones affected by this senseless violence in Las Vegas, Karen [Pence] & I are praying for you & offering our love. The hearts & prayers of the American people are with you. You have our condolences and sympathies.”

The victims were apparently shot with a high-powered assault rifle from the 32nd floor of the Mandalay Bay Hotel, with police confirming shortly after midnight that Paddock had died in a standoff with authorities.

Singer Jason Aldean was performing onstage when shots were first fired. He later confirmed on Instagram that he and his band were safe. The hotel and the concert are located on the Las Vegas Strip, one of the city’s most popular tourist attractions.

“The president has been briefed on the horrific tragedy in Las Vegas. We are monitoring the situation closely and offer our full support to state and local officials,” White House press secretary Sarah Sanders said in a statement Monday morning. “All of those affected are in our thoughts and prayers.”