At least one gunman has opened fire at a Texas high school, killing eight to 10 people, most of them pupils, authorities said.
Harris County Sheriff Ed Gonzalez said he could not be precise about the number of deaths at Santa Fe High School.
Two suspects believed to be students are in custody.
Authorities said possible explosive devices have been found at the school and experts are in the process of rendering them safe.
There’s no indication how many devices have been found. Police asked the public to “remain vigilant” and to call 911 if they see any suspicious items.
It was the nation’s deadliest school shooting since the February attack in Parkland, Florida, that killed 17 people and re-energised the gun-control movement after surviving teenagers launched a campaign for reform.
School officials confirmed an unspecified number of injuries but would not release further details.
A school police officer is being treated in hospital, the sheriff said, but there was no immediate word on the extent of his injuries.
“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 residents about 30 miles south east of Houston.
School officials said police were working to secure the building and move pupils to another location to reunite with their parents.
One student told Houston television station KTRK in a telephone interview that a gunman came into her first-period art class and started shooting. She 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.
She said she did not get a good look at the gunman because she was running away. She said students escaped through a door at the back of the classroom.
The Bureau of Alcohol, Tobacco, Firearms and Explosives said it was responding to the shooting.
School shooting in Texas. Early reports not looking good. God bless all!— Donald J. Trump (@realDonaldTrump) May 18, 2018
After the February 14 attack on Marjory Stoneman Douglas High School, survivors pulled all-nighters, petitioned city councils and state legislators, and organised protests in a grassroots movement.
Within weeks, state legislators adopted changes, including new weapons restrictions. The move cemented the gun-friendly state’s break with the National Rifle Association, and the NRA fought back with a lawsuit.
In late March, the teenagers spearheaded one of the largest student protest marches since Vietnam in Washington and inspired hundreds of other marches from California to Japan.