Posting on his Truth Social platform, the President said the shooter has been "apprehended" and called for the event to resume. He also praised the Secret Service for acting "quickly and bravely".
Trump wrote: "Quite an evening in D.C. Secret Service and Law Enforcement did a fantastic job. They acted quickly and bravely.
"The shooter has been apprehended, and I have recommended that we “LET THE SHOW GO ON” but, will entirely be guided by Law Enforcement. They will make a decision shortly.
"Regardless of that decision, the evening will be much different than planned, and we’ll just, plain, have to do it again. President DONALD J. TRUMP."
The President and First Lady and all other Secret Service protectees are safe, Secret Service spokesman Anthony Guglielmi has said. One individual - whose condition is unknown - is in custody, he says.
President Trump has left the venue after the suspected shooting. "The First Lady, plus the Vice President, and all Cabinet members, are in perfect condition," he wrote on Truth Social.
The event will be delayed and rescheduled within 30 days, he added.
He will deliver a statement to the media shortly after 10pm local time.
