A man has been arrested after a foil package containing a mystery powder was tossed into the Premier’s Rockingham electorate office just days out from the State Election.

One staffer was taken to hospital on Tuesday afternoon while others were evacuated.

A similar incident took place at a Federal Labor MP’s office, also in Rockingham.

WA Police Commissioner Chris Dawson said the substance found inside both packages was not harmful.

The 67-year-old suspect is currently undergoing a mental health assessment.