A 14-year-old girl arrived at Dunbarton High School this morning wielding two knives and started attacking students in the hallway, Durham Regional Police say.

Nine people, including three teachers, sustained injuries at the school in Pickering, Ont., police said. Four were taken to hospital, including one who suffered serious injuries. None of the victims' injuries are considered life-threatening, police said.

It did not appear any particular student or staff member was targeted.

Officers were called to the school around 8:30 a.m. ET for reports of a stabbing inside the school. Upon arrival, police arrested a girl whom two staff members had wrestled to the floor. Charges are pending, police said.

Classes will resume Wednesday morning, the school said in a statement, commending staff and students for "great leadership, courage and co-operation" and the police response.

Durham Regional Police say six students and three teachers were stabbed Tuesday at Dunbarton High School in Pickering, Ont., east of Toronto. (Nicholas Boisvert/CBC)

The high school, which is on Sheppard Avenue near Whites Road, remained on lockdown for several hours Tuesday morning as officers went room to room looking for students who witnessed the attack. Students who didn't see anything were released from the school, and the lockdown was lifted just after 10 a.m.

The school will be closed for the rest of the day.

Pickering is a city of about 94,000 located east of Toronto.

"I saw a girl with two knives, steak knives, and she was holding one above the other," said Kristine Petrovska, a student who was inside the school when the incident occurred. "She was maybe a metre away from me."

One 14-year-old girl said she came face to face with the attacker, who made slashing motions with the knives in her direction.

"I just ran for my life," the girl said as she began to cry. "I just can't believe it happened. She almost got me."

Students ran in all directions

Zakyr Rhemtulla, a Grade 9 student, said he witnessed chaos from the moment he arrived at school Tuesday morning.

He said as soon as he opened the front door, he saw students running in all directions.

"I'm like 'Oh, what's happening,"' he said in a telephone interview. "So, I just kept on walking, and some teacher told me, 'Oh, come into this room.' So, I ran into the room. They locked the door, closed the curtains, turned the lights off."

Rhemtulla and a few other students remained in the classroom while the school was in lockdown and police combed the property for evidence.

He said the initial shock of the situation eased as students monitored social media and learned that no one appeared to be in danger.