The shooter, a student and identified as Jaylen Fryberg, shot himself dead after going on a shooting spree in the cafeteria of Marysville Pilchuck High School, north of Seattle, Xinhua quoted officials as saying.
Though the shooting's motive is being investigated, witnesses said the tragedy followed a fight at the school among youngsters.
According to CNN, Fryberg who opened fire at the Marysville-Pilchuck High School, played football and was recently named to the homecoming court.
He was crowned freshman class homecoming prince.
Fryberg was in the school's cafeteria, went up to a table with students, "came up from behind ... and fired about six bullets into the backs of them," witness Jordan Luton told CNN. "They were his friends, so it wasn't just random," Luton said.
The gun used in the shooting has been traced to Fryberg's father, a law enforcement source with knowledge of the investigation.
The incident took place about 10:45 a.m. (1745 GMT). Live video footage from the scene showed police officers escorting students out of school buildings.
The school has some 2,500 students. The Marysville School District posted a message on its website announcing that students were being relocated to a community church and school buses would send them home.