Emergency services were called to Willetton Senior High School at 11.15am on Monday.

Police would not confirm reports the teacher was stabbed but confirmed she received a "minor wound" and was taken to Fiona Stanley Hospital for treatment.

The student accused of the attack fled the school grounds and was being sought.

State School Teachers' Union of WA president Pat Byrne said she was deeply disturbed by the incident.

"Every teacher should be able to go to work confident that they will be safe from harm," she said.

"This incident is a reminder of the dangers teachers face and the need for constant improvements around safety in schools."

Worried parents took to social media after receiving text messages from their children who were placed in lockdown at the school.

"It was a little worrying getting a text from my daughter this morning of her in a classroom, with all the lights off, having to keep quiet," one mum wrote.

"Definitely an experience for both my kids. Hopefully one they don't have to go through again."

Australian Associated Press