A shooter opened fire at a high school in Washington state on Wednesday, killing one person and injuring at least three others, authorities said.

Brian Schaeffer of the Spokane Fire Department told reporters that one person died at Freeman High School in the tiny town of Rockford, south of Spokane, and three injured victims were taken to a hospital.

Providence Sacred Heart Medical Centre and Children's Hospital received three paediatric patients, spokeswoman Nicole Stewart said. They were in stable condition, and family members were with them, she said.

Spokane County Sheriff Ozzie Knezovich said at the scene that the shooter was in custody, The Spokesman-Review newspaper reported.

Worried parents rushed to the school in the town of about 500 people near the Idaho border, about 25 miles southeast of Spokane. The two-lane road into town was clogged as people sped to the school.

Cheryl Moser said her son, a freshman at Freeman High School, called her from a classroom after hearing shots fired.

“He called me and said, 'Mom there are gunshots.' He sounded so scared. I've never heard him like that,” Moser told the newspaper. “You never think about something happening like this at a small school.”

Ambulances and a Life-flight helicopter were sent to the school.

Stephanie Lutje told The Associated Press that she was relieved to hear her son was safe after his high school near Freeman was put on lockdown. She commended the school district for its communication with parents.

“It's been amazing, within probably 15-20 minutes of hearing about it, I'd already received a phone call, I'd already received a text message saying that their school is okay,” she said.

She was still worried for others she knew, including a co-worker who had yet to hear from her son, a sophomore at Freeman.

“My stomach's in knots right now,” she said.

Washington Governor Jay Inslee said in a statement that “all Washingtonians are thinking of the victims and their families, and are grateful for the service of school staff and first responders working to keep our students safe.”