Explosive devices have also been found both on and off the campus and are currently being made safe by authorities.
The shooter, who reportedly was armed with pipe bombs, has been arrested after exchanging fire with police at Santa Fe High School, in Texas.
Law enforcement officials have confirmed that the shooter was a 17-year-old student, reports KHOU 11.
The news outlet is also reporting a mobile home has been surrounded which is suspected to be the home of the shooter.
Santa Fe Independent School District Police chief Walter Braun told a press conference there there had been "multiple fatalities" but while the exact number was not yet known he said he believed it was "fewer than ten".
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."
He said a Santa Fe school police officer was among the injured.
The school's assistant principal Cris Richardson said a suspect had been arrested.
Richardson said: "We hope the worst is over, and I really can't say any more about that because it would be pure speculation."
A witness told CNN that the shooter entered an art class and opened fire hitting one girl in the leg.
The teen suspect shot three people inside the classroom prompting other students to flee before the gunman opened fire in other parts of the campus, reports local media.
One witness reportedly said the suspect was armed with a pistol and a shotgun and "always walked around in a trench coat".
At least one police officer was wounded during the gun fight with the youngster, according to reports.
WHAT WE KNOW SO FAR
- Student walked into an art classroom in Santa Fe High School, in Texas, opened fire shooting at least three people as pupils fled in terror
- Unnamed teen gunman was reportedly armed with a sawn off shotgun and a pistol
- The suspect has been arrested after a shootout with police
- Student said he "always walked around in a trench coat"
- Unconfirmed claims that shooter was armed with "pipe bombs"
- At least ten people have reportedly been killed
- One of the teachers, who is an ex-Marine, pulled the fire alarm at around 7.45am in effort to warn of active shooter.
- Angelica Martinez, a 14-year-old student, said: “We started hearing gunshots. Everybody starts running, but like the teachers are telling us to stay put, but we're all just running away."
- President Trump tweeted: “School shooting in Texas. Early reports not looking good. God bless all!”
Footage from a CBS news helicopter shows dozens of teens being evacuated on the grass outside the school.
A student said that a teacher, who is a former US marine, pulled the fire alarm to alert others, reports KTRK.
Student Leila Butler told ABC13 that the alarms sounded at around 7.45am local time prompting teenagers to flee their classrooms.
She told the news outlet that she heard gun shots being fired and is currently sheltering with teachers and fellow students near the campus.
Speaking to CNN, student Angelica Martinez, 14, said she heard gunshots after being evacuated.
She said: "We were all standing (outside), but not even five minutes later, we started hearing gunshots.
"And then everybody starts running, but like the teachers are telling us to stay put, but we're all just running away."
"I didn't see anybody shooting, but like (the gunshots) were kind of spaced.”
Angelica said she heard about four shots.
Two hospitals south of Houston said they had received nine patients from the school shooting.
Clear Lake Regional Medical Center said it admitted seven, and Mainland Medical Center received two.
President Donald Trump, speaking at a prison reform event at the White House, described the attack as "absolutely horrific".
He said: "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."
Santa Fe, which is 30 miles outside of Houston, has a population of around 13,000 while the school has about 1,400 students, according to GreatSchool.org.
The death toll makes events in Santa Fe the deadliest school shooting since the one in February at Parkland, Florida when 17 people were killed.
Source: Read Full Article