There was no immediate sign of anyone else badly hurt or of any other suspects involved in the shooting at Reynolds High School in the town of Troutdale, a middle-class suburb of Portland, police said.
The school was immediately placed on a security lockdown, then evacuated room-by-room as law enforcement and emergency personnel converged on the campus of 2,800 students, which is due to hold its last day of classes on Wednesday before the summer break.
"A gunman entered the high school this morning, shot one student. Unfortunately, that student has died," Troutdale Police Chief Scott Anderson said at a news conference. "The gunman was located and the gunman is also deceased."
Anderson did not identify the gunman, give his age or say whether he was a student. Authorities also did not say how the suspect died.
Two girls from the high school, sisters Kadejah and Deondra Nixon, told Reuters after being reunited with their parents that police were asking students whether anyone had ridden a bus to school with a student carrying a guitar case.
Multnomah County Sheriff’s Lieutenant Steve Alexander said authorities were methodically combing through the school to be sure no one else was injured.
“My understanding, we’re still investigating, they’re still going through the school. The initial indications are that is it,” he said. The violence in northern Oregon was the latest in a string of U.S. fatal shootings in public places since May, including a shooting at a Christian college in neighboring Washington state last week.
U.S. Representative Earl Blumenauer, a Democrat from Oregon's 3rd congressional district, expressed the growing frustration of many politicians with the spate of gun violence in a Twitter message: "Another shooting. I always hope tragedy will inspire action. Simple common sense steps make (a) difference. Start w/universal background checks."
Television footage at the Oregon school showed police officers in helmets and tactical gear, stepping from armored vehicles and running near the school’s perimeter with rifles. Students were seen streaming out of the school with their hands raised.
A few miles away, students bused from the campus were being reunited with anxious parents in the parking lot of a nearby shopping center.
"I'm glad it wasn't worse," said Rachelle Rueschenberg, a mother clutching her ninth-grade daughter, Maddy. "It's so hard."
Kadejah Nixon said she did not hear gunfire - the shooting was in a different wing of the school from where she was located - but she recounted that an announcement over the school's public address system abruptly urged all students to go to the nearest classroom and close the doors.
"'This is not a drill, this is serious, get into a classroom,'" she quoted the announcement as saying.