Two teens hospitalised, four arrested after gas allegedly sprayed at WA school

Two teenage boys have been taken to hospital and four students have been arrested after gas believed to be pepper spray was allegedly sprayed at a high school in Perth.

Ellenbrook Secondary College in the city's north-eastern suburbs was evacuated this afternoon and students and teachers were treated on the grounds by ambulance officers.

The gas is believed to have been deployed through the air vent of a year 9 classroom about 1.20pm (3.20pm AEST), sending the school into lockdown.

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Senior Sergeant John Browne said police were treating the incident as "significant".

"It does pose some risk to the wider school with recirculation of air," he said.

Two teenagers were rushed to Midland Hospital while four teenagers and seven teachers were treated at the scene by paramedics.

"I believe there was some itchiness of the eyes and increased heart rate and some difficulty breathing," Browne said.

Browne said police were looking for the canister and taking air samples at the school, while four students were being questioned.

"If we're able to clearly establish who is responsible for this particular incident then most definitely there will be charges," Browne said.