SANTA FE, Texas (AP) — At least one gunman opened fire at a Houston-area high school Friday, killing eight to 10 people, most of them students, authorities said, in the nation’s deadliest such attack since the massacre in Florida that gave rise to a campaign by teens for gun control.

Harris County Sheriff Ed Gonzalez said he could not be precise about the number of deaths at Santa Fe High School, which went on lockdown around 8 a.m. One person was in custody, and a second person had been detained, he said.

An unknown number of possible explosive devices were 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 see anything suspicious.

The district confirmed an unspecified number of injuries but did not release details. A school police officer was shot, officials said, but there was no immediate word on his condition.

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!”

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.

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