President Donald Trump has been briefed on the shooting in Las Vegas, which has left at least 50 dead and 200 injured, White House press secretary Sarah Sanders said in a statement Monday morning.
"The President has been briefed on the horrific tragedy in Las Vegas," Sanders said. "We are monitoring the situation closely and offer our full support to state and local officials. All of those affected are in our thoughts and prayers."
Trump tweeted shortly after Sanders' statement, writing: "My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you!"
An administration official told CNN the President's trip to Puerto Rico to survey the hurricane response there, which was planned for Tuesday, is now under review.
Nevada politicians also responded Monday morning to the massacre, decrying the violence and offering thanks to first responders.
"Senseless, horrifying act of violence in Las Vegas tonight," Republican Sen. Dean Heller tweeted. " Praying for all the victims & those impacted by the tragedy."
"Thankful for police and first-responders on the scene," Heller said.
Heller said he had spoken with Nevada Gov. Brian Sandoval and state Attorney General Adam Laxalt.
Sandoval, a Republican, called the shooting a "tragic & heinous act of violence" and offered his prayers.
"A tragic & heinous act of violence has shaken the #Nevada family. Our prayers are w/ the victims & all affected by this act of cowardice," Sandoval tweeted.
Members of Nevada's House delegation offered their thoughts as well.
Democratic Rep. Ruben Kihuen thanked the first responders in a tweet, and Rep. Dina Titus, also a Democrat, said in a statement that her "heart aches for the victims, their loved ones and our community."
Foreign leaders sent their condolences on the shooting Monday morning. United Kingdom Prime Minister Theresa May responded on Twitter, as did London Mayor Sadiq Khan.
"PM -- The UK's thoughts are with the victims and the emergency services responding to the appalling attack in Las Vegas," May tweeted.
Khan tweeted, "A deeply sad day for the city of Las Vegas. London sends our condolences to the victims and their families."
Police said in the early hours of Monday morning that the suspected gunman, identified as Stephen Paddock, 64, had been killed following what has now become the deadliest mass shooting in US history. At least 50 people died and 200 were injured, police said.