Police probe possible SA school threat

Police are investigating written threats to harm teachers and damage property at a South Australian school.

The two-page typed letter was discovered on Thursday at the administration building of Peterborough High School, in the state's mid-north.

Police say that, as per set procedures, the threat is being taken seriously and the letter is being forensically examined.

"Extra police patrols will be sent to the area and additional security measures will be put in place," they said in a statement.