Speaking from the White House hours later, a visibly shaken U.S. President Joe Biden urged Americans to stand up to the politically powerful US gun lobby, which he blamed for blocking enactment of tougher firearms safety laws.
Biden ordered flags flown at half-staff daily until sunset on Saturday in observance of the tragedy.
“As a nation, we have to ask, 'When in God's name are we going to stand up to the gun lobby?'” Biden said on national television, suggesting reinstating a US ban on assault-style weapons and other “common sense gun laws.”
Mass shootings in America have frequently led to public protests and calls for stricter background checks on gun sales and other firearm controls common in other countries, but such measures have repeatedly failed in the face of strong Republican-led opposition.
Authorities said the suspect in Tuesday's killings acted alone. Governor Greg Abbott said that the shooter was apparently killed by police who confronted him at the school, and that two officers were struck by gunfire, though the governor said their injuries were not serious.
After conflicting early accounts of the death toll, Texas public safety officials said Tuesday night that 19 schoolchildren and two teachers had died.
The community, deep in the state's Hill Country region, has about 16,000 residents, nearly 80% of them Hispanic or Latino, according to U.S. Census data.