The suspect has been identified as a 17-year-old male student from the school. US President Donald Trump has expressed "sadness and heartbreak" over the incident.
A gunman opened fire at Santa Fe High School in Texas on Friday, killing 10 people, including students.
The incident is the latest in a series of shootings at US schools and universities. In February, a gunman killed 17 students and staff members at a Florida high school, intensifying a national debate over gun control and gun rights.
What we know so far
Trump expresses 'heartbreak'
US President Donald Trump expressed "sadness and heartbreak" over the incident.
Trump described it as "absolutely horrific" and said, "This has been going on too long in our country."
"My administration is determined to do everything in our power to protect our students, secure our schools, and to keep weapons out of the hands of those who pose a threat to themselves, and to others," he added.
Vice President Mike Pence said he and the president were monitoring the situation.
Governor Abbott called Friday's shooting "one of the most heinous attacks that we've ever seen in the history of Texas schools."
Mass shootings: The United States, where the right to bear arms is enshrined in the constitution, has struggled with gun violence for decades. The country has seen more than 100 mass shootings this year, with nearly 130 killed, according to the Gun Violence Archive, a database that tracks gun violence incidents. It classifies mass shootings as events in which four or more people were shot at around the same time and place.
ap/msh (Reuters, AP, AFP)