At least eight people were killed when a male student opened fire at a Texas high school on Friday, a local sheriff said, as President Donald Trump expressed his "heartbreak" over the "horrific" shooting.
The incident took place at Santa Fe High School in the city of the same name, located about 30 miles (50 kilometers) southeast of Houston.
"There are multiple fatalities," the sheriff of Harris County, Ed Gonzalez, told a news briefing. "There could be anywhere between eight to 10, the majority being students."
The male teen suspect in custody was not immediately identified. A second possible person of interest was being questioned, Gonzalez told reporters.
A somber Trump, who was speaking at an event on prison reform at the White House, expressed "sadness and heartbreak" over the deadly shooting spree.
"This has been going on too long in our country," Trump said. "We're with you in this tragic hour."
The shooting was the latest in what has become an all-too-familiar situation in American schools, where gun violence has become a part of everyday life.
Earlier this year, 17 students and staff were killed in a shooting at a Florida high school -- a massacre that prompted survivors to launch a grassroots campaign against gun violence.
The US president, who has previously shied away from gun control measures in favor of arming teachers, said his administration was "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."
The shooting erupted before 8:00 am, as the school day was beginning.
"There was someone that walked in with a shotgun and started shooting, and this girl got shot in the leg," an eyewitness identified as Nikki told local television station KTRK.
She said students fled the school in a panic, and several other students told local media they heard multiple gunshots.
The school district, which quickly imposed a lockdown, cleared the students from the campus, with television footage showing them leaving in a single file. No other schools had been affected.
Some students were evacuated to a nearby auto shop, where parents were picking up their children, according to CBS affiliate KHOU-TV.
Parent Richard Allen told KTRK he arrived at the school soon after the shooting and reported seeing a number of victims being taken away in ambulances.
"My son said someone went into the art room and started shooting a lot of the kids," Allen said.
Student Paige Curry told local media that she heard gunshots and then a fire alarm, after which students were taken out by teachers to a nearby gas station.
"I saw some girl -- she had, you know, she got shot in the kneecap, I guess. So she had a bandage around it. She was limping and then the firemen came and got her," another student, who gave his first name as Tyler, told CBS.
A large contingent of police as well as agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives were responding to the incident.