Texas Gov. Greg Abbott says 10 people are dead and 10 more wounded after a shooting at a high school in the town of Santa Fe, the nation's deadliest such attack since the massacre in Florida that gave rise to a campaign by teens for gun control.
Several law enforcement officials told NBC News that nine students and one teacher died in the shooting.
Abbott called Friday's shooting "one of the most heinous attacks that we've ever seen in the history of Texas schools."
The governor said the suspect had a shotgun and .38 revolver, which appeared to be legally owned by the suspect's father. He says explosive devices including a molotov cocktail that had been found in the suspected shooter's home and a vehicle as well as around the school and nearby.
A law enforcement official told NBC that four pipe bombs were found inside the school. Officials said, however, that none of the devices exploded and that it wasn't clear whether any of them were fully capable.
The governor says the suspect said he originally intended to commit suicide but gave himself up and told authorities that he didn't have the courage to take his own life.
Abbott said there are "one or two" other people of interest being interviewed about the shooting.
The governor said there were few prior warnings about the suspected gunman, unlike in other recent mass shootings.
Galveston County Sheriff Henry Trochesset says 17-year-old Dimitrios Pagourtzis has been charged with capital murder.
Abbott said that "unlike Parkland, unlike Sutherland Springs, there were not those types of warning signs." He was referring to the Feb. 14 school shooting in Florida and one in November inside a church in a town near San Antonio.
Abbott says "the red-flag warnings were either non-existent, or very imperceptible" in the case of the suspected Santa Fe shooter.
A woman who answered the phone at a number associated with the Pagourtzis family declined to speak with the AP.
She said: "Give us our time right now, thank you."
Pagourtzis plays on the Santa Fe High School junior varsity football team, and is a member of a dance squad with a local Greek Orthodox church.
A hospital spokesman says a school resource officer who was shot in the arm when he engaged the gunman is undergoing surgery.
David Marshall, the University of Texas Medical Branch's chief nursing officer, says Santa Fe school resource officer John Barnes is in stable condition Friday afternoon.
Marshall says a bullet hit Barnes' arm, damaging the bone and a major blood vessel around his elbow. He says the blood vessel has been repaired, and that Barnes is expected to emerge from surgery within a few hours.
Michael Farina, 17, said he was on the other side of campus when the shooting began and thought it was a fire drill. He was holding a door open for special education students in wheelchairs when a principal came bounding down the hall and telling everyone to run. Another teacher yelled out, "It is real."
Students were led to take cover behind a car shop across the street from the school. Some still did not feel safe and began jumping the fence behind the shop to run even farther away, Farina said.
"I debated doing that myself," he said.
Friday's assault was the deadliest in Texas since a man with an assault rifle attacked a rural church late last year, killing more than two dozen people. It comes three months after the Feb. 14 attack in Parkland, Florida, that killed 17.
Aerial footage showed students standing in a grassy field and three medical helicopters landing at the school in Santa Fe, a city of about 13,000 people roughly 30 miles (48 kilometers) southeast of Houston.
One student told Houston television station KTRK in a telephone interview that a gunman came into her first-period art class and started shooting. The student said she saw one girl with blood on her leg as the class evacuated the room.
"We thought it was a fire drill at first but really, the teacher said, 'Start running,'" the student told the television station.
The student said she did not get a good look at the shooter because she was running away. She said students escaped through a door at the back of the classroom.
Authorities did not immediately confirm that report.
Vice President Mike Pence said he and President Donald Trump were briefed on the shooting. Pence said the students, families, teachers and all those affected should know: "'We're with you. You're in our prayers and I know you are in the prayers of the American people."
Trump added in a tweet that that early reports were "not looking good. God bless all!"
Trump has ordered that U.S. flags fly at half-staff as a mark of "solemn respect" for those affected by the school shooting.
Flags are to be flown at half-staff until sunset on May 22. The order applies to the White House and all public buildings and grounds, military posts and naval stations and vessels, as well as at U.S. embassies, consular offices and other facilities abroad. The flag atop the White House was immediately lowered on Friday.
First lady Melania Trump also weighed in on Twitter, saying her "heart goes out to Santa Fe and all of Texas today."
The shooting was all but certain to re-ignite the national debate over gun regulations. In the aftermath of the Feb. 14 attack on Marjory Stoneman Douglas High School, survivors pulled all-nighters, petitioned city councils and state lawmakers, and organized protests in a grass-roots movement.
Within weeks, state lawmakers adopted changes, including new weapons restrictions. The move cemented the gun-friendly state's break with the National Rifle Association. The NRA fought back with a lawsuit.
In late March, the teens spearheaded one of the largest student protest marches since Vietnam in Washington and inspired hundreds of other marches from California to Japan.
Parkland survivors took to social media to express outrage and heartbreak over the Texas attack.
"My heart is so heavy for the students of Santa Fe High School. It's an all too familiar feeling no one should have to experience. I am so sorry this epidemic touched your town — Parkland will stand with you now and forever," Marjory Stoneman Douglas student Jaclyn Corin said in a tweet.
She also directed her frustration at Trump, writing "Our children are being MURDERED and you're treating this like a game. This is the 22nd school shooting just this year. DO SOMETHING."
The calls for tighter gun controls that have swelled since the February mass shooting at a Florida high school have barely registered in gun-loving Texas — at least to this point.
Texas has some of the country's most permissive gun laws and just hosted the NRA's annual conference earlier this month. In the run-up to Texas' march primaries, gun control was not a main issue with candidates of either party. Republicans did not soften their views on guns, and Democrats campaigned on a range of issues instead of zeroing in on gun violence.
— CNBC.com contributed to this report.