Four students and an adult security guard were taken to hospital after the incident at Foss High School, according to the Tacoma Fire and Tacoma Police departments, Xinhua reported.
Firefighters and police officers responded shortly before 1:40 pm local time following reports of an altercation or a possible stabbing.
The school was temporarily placed on lockdown after the incident. Police said the scene had been secured and officers were working with the school to reunite students with their families.
The circumstances surrounding the incident remain under investigation.