WATCH LIVE: Trump to make national address after Florida school shooting
President Donald Trump pauses during the 9/11 Observance Ceremony at the Pentagon in Washington, D.C. (DOD photo by Navy Petty Officer 1st Class Dominique A. Pineiro)

U.S. President Donald Trump will make a national address at 11 a.m. ET on Thursday, a White House spokeswoman said, about a massacre at a Florida high school on Wednesday in which a 19-year-old gunman killed 17 people in one of the country's deadliest school shootings.


Earlier on Thursday, Trump wrote in a Twitter post: "So many signs that the Florida shooter was mentally disturbed, even expelled from school for bad and erratic behavior. Neighbors and classmates knew he was a big problem. Must always report such instances to authorities, again and again!"

(Reporting by Makini BriceEditing by Chizu Nomiyama)