A 14-year-old student has been arrested after entering a Pickering, Ont. high school armed with two large knives and injuring nine people in what police believe was a random attack.

The Durham District School Board said six students and three staff members at Dunbarton High School were injured in the stabbings, which occurred shortly after 8:30 a.m. on Tuesday.

The teen attended the school with two knives, and "started attacking students in the hallways," Durham Regional Police said in a statement. Two staff members located the girl, and were able to hold her down until police arrived.

Nine people were injured before she was stopped, police said, explaining that investigators do not believe any particular students of staff members were targeted.

Four of the victims were transported to hospital, but none of their injuries are life-threatening, police said.

A 14-year-old female student who attends the high school has been arrested. Police say the student is the lone suspect.

The suspect, whose identity is protected under the Youth Criminal Justice Act, will not be named.

"It seems to be random at this point," Sgt. Bill Calder told reporters at the scene. "It doesn’t seem to be targeted."

Calder said two staff members managed to stop the suspect and contain her until police arrived.

"This is a safe school by nature," Calder said, adding, "(the staff members) did a great job of ending this very quickly."

The Durham District School Board said students were being released one class at a time, to ensure that all witnesses are able to speak to police.

Counselling services will be made available to students, and classes will resume on Wednesday.

"People have suffered physical injuries, but we never take light of the fact there's other things we have to look into, like emotional well-being," Calder said.

Police said a lockdown at the school, imposed as police searched each room in the school for victims and other potential suspects, is slowly being lifted.

Ontario Premier Kathleen Wynne said the stabbing was "incredibly worrisome."

"I know that the police are doing everything that they can and they're in control of the situation," she told reporters on Tuesday.

The investigation is ongoing, and police ask anyone with more information to call 1-888-579-1520, ext. 2528. Tips can also be left anonymously through Crime Stoppers at 1-800-222-8477 (TIPS).