Ten people have been killed and 10 others are injured after a shooting by a student at a Texas high school, says the state governor.
Harris County Sheriff Ed Gonzalez told reporters the majority of the dead at Santa Fe High School were students.
The suspect is in custody and he is 17-year-old Dimitrios Pagourtzis, according to CBS News.
Police said explosive devices were found at the school, 40 miles (65km) south of Houston, and off-campus.
Governor Greg Abbott said the suspect used a shotgun and a .38 revolver that he appeared to have taken from his father, who legally owned the weapons.
He said it was “one of the most heinous attacks that we’ve ever seen in the history of Texas schools”.
“It’s impossible to describe the magnitude of the evil of someone who would attack innocent children in a school.”
He added that “various kinds of explosive devices” have been found, including “a CO2 device” and “a Molotov cocktail”, which typically consists of a bottle filled with flammable liquid.
Santa Fe Police Chief Jeff Powell said: “There have been explosive devices found inside the high school, and in the surrounding areas adjacent to the high school.”
Chief Powell advised residents to be aware of any suspicious objects they find.
“Do not touch any items that look out of place,” he said, warning residents to immediately call police.
Santa Fe school police officer John Barnes has been named among the injured.
Officer Barnes is in a critical condition and undergoing surgery, according to local media.
How the attack unfolded
Students said the shooter entered an art class and started shooting shortly before 08:00 local time.
A student told local network KHOU-11 that a teacher who realised what was happening “ran out of the classroom and he pulled the fire alarm” to “get the rest of the school out”.
There were 1,400 students in the school at the time of the attack, according to Lt Gov Dan Patrick.
One witness told KTRK-TV the shooting happened in her art class, and that one of the victims was a girl.
“There was someone that walked in with a shotgun and started shooting,” the student said, “and this girl got shot in the leg.”
A bomb squad was sent to the scene, and several helicopter ambulances flew victims to hospital.
Federal officials with the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) were helping the investigation.
What’s the reaction been?
School superintendent Dr Leigh Wall said in a statement: “We experienced an unthinkable tragedy at our high school this morning.”
President Donald Trump, speaking at a prison reform event at the White House, described the attack as “absolutely horrific”.
“My administration is 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,” he added.
Texas Governor Greg Abbott called the shooting the “most heinous attack” in Texas school history during a news conference.
Two weeks ago, Mr Trump reiterated his call to arm teachers with guns during a speech in Dallas to the National Rifle Association (NRA).
First Lady Melania Trump tweeted: “My heart goes out of Santa Fe and all of Texas today.”
Shortly after the shooting began in the town of about 13,000 residents, a man carrying an American flag, wearing a Trump hat, and carrying a pistol on his hip approached news cameras.
The man, who did not give his name, said his goal was to “get to the school. Make America great again”.
Another man then told reporters “we need prayers”.
“This idiot is walking down the street with a damned pistol on his side where we just had kids get shot,” he said referring to the other man.
“I’m a guns rights person. I have guns. But this idiot is walking down here and saying he needs to make America great again. That’s not what America needs.”
How do previous school shootings compare?
The Texas attack is the deadliest school shooting since the one in February at Parkland, Florida.
That attack left 17 dead and spawned a nationwide youth-led campaign for gun control.
Earlier this week, a police officer was able to stop a former student who opened fire at an Illinois high school before anyone was injured.
More on US gun violence
Santa Fe High School: Ten dead in shooting