Two people are in custody after an unknown substance was sprayed at customers and staff at a Bunnings store in the West Australian town of Northam.
The store was evacuated by staff following the incident about 2.30pm on Anzac Day.
"Several people were affected with a burning sensation to their eyes, nose and throats and were treated in hospital as a precaution," WA Police said in a statement.
Police arrested two people, one of whom is alleged to have sprayed the unknown substance at customers and staff.
The West Australian newspaper reported seven women, two teenage girls and a man were rushed to Northam Regional Hospital for treatment.
Inquiries are continuing.