A gunman opened fire at an elementary school in South Texas on Tuesday, killing 19 students and two adults, before the suspect himself died, the state police said on Tuesday.

U.S. President Joe Biden has implored the nation to stand up to the gun lobbies and "turn pain to action" following the deadly shooting.

UN Secretary-General Antonio Guterres was deeply shocked by the shooting and extended his condolences to the families and loved ones of the victims and to the entire community.

Flags at the White House were lowered to half-staff on Tuesday, live footage showed.