Six people were injured, including several who were stabbed, in an altercation at a Washington state high school Thursday, authorities said.

Four were in serious condition and two sustained non life-threatening injuries, a spokeswoman for the Tacoma Fire Department said earlier Thursday. All were in stable condition Thursday night, it said.

Several of the injured people were stabbed, Tacoma police told NBC affiliate KING of Seattle.

Officer Shelbie Boyd, a Tacoma police spokesperson, said they were injured during an altercation at Foss High School. Five of the people are students, including the suspect, and one is a security guard, Boyd said.

Boyd said the suspect, who has not been publicly identified, is in custody. She said it was unclear what prompted the altercation.

Emergency personnel responded to the school at 1:38 p.m., said the fire department spokeswoman, Chelsea Shepherd.

Video from KING showed a large police presence outside the school, which was placed on lockdown, Boyd said.

Tacoma Public Schools thanked its staff and first responders in a statement and said school and after-school activities for Friday are canceled.

"This incident is still under investigation and discipline have not yet been determined," the statement said. (NBC News)