A gunman carrying a shotgun and a revolver has opened fire at a Houston-area high school, killing 10 people, most of them students, authorities say.
- Explosive devices, including a molotov cocktail, were also found at the scene
- Students fled across the road to hide at auto store
- Victims of Parkland, Florida, school shooting "stand with" Texas students
It was the United States' deadliest such attack since the massacre in Florida that gave rise to a campaign by teens for gun control.
The suspected shooter, who was in custody, also had explosive devices, including a molotov cocktail, that were found in the school and nearby, said Texas Governor Greg Abbott, who called the assault "one of the most heinous attacks that we've ever seen in the history of Texas schools".
The assailant intended to kill himself but gave up and told authorities that he did not have the courage to take his own life, Mr Abbott said.
Another 10 people were wounded at the school in Santa Fe, a city of about 13,000 people roughly 48 kilometres south-east of Houston.
One hospital reported treating eight wounded patients. Six were treated and released. One was listed in critical condition, and another in fair condition.
Harris County Sheriff Ed Gonzalez said a second person had also been detained.
Two law enforcement officials have identified a person in custody in the Houston-area school shooting as 17-year-old Dimitrios Pagourtzis.
An unknown number of possible explosive devices was found at the school and off campus.
Authorities were in the process of rendering them safe and asked the public to call 911 if they saw anything suspicious.
The district confirmed an unspecified number of injuries but said it would not immediately release further details.
A school police officer was shot, officials said, but there was no immediate word on his condition.
"We hope the worst is over, and I really can't say any more about that because it would be pure speculation," Assistant Principal Cris Richardson told reporters at the scene.
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 48 kilometres south-east of Houston.
School officials said law enforcement officers were working to secure the building and move students to another location.
Students were being transported to another location to reunite with their parents.
'It is real'
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 an auto store 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, Mr Farina said.
"I debated doing that myself," he said.
Another 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.
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 February 14 attack in Parkland, Florida, that killed 17.
External Link: We grieve for the terrible loss of life, and send our support and love to everyone affected by this horrible attack in Texas. To the students, families, teachers and personnel at Santa Fe High School – we are with you in this tragic hour, and we will be with you forever
US Vice-President Mike Pence said he and President Donald Trump were briefed on the shooting.
Mr 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."
Mr Trump added in a tweet that early reports were "not looking good. God bless all".
First lady Melania Trump also weighed in on Twitter, saying her "heart goes out to Santa Fe and all of Texas today".
'An all too familiar feeling'
The shooting is all but certain to re-ignite the national debate over gun regulations.
In the aftermath of the attack on Marjory Stoneman Douglas High School, survivors petitioned city councils and state politicians, and organised protests in a grass-roots movement.
Within weeks, state politicians 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," Marjory Stoneman Douglas student Jaclyn Corin said in a tweet.
"I am so sorry this epidemic touched your town — Parkland will stand with you now and forever."
She also directed her frustration at Mr 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.