The RAC Rescue helicopter was sent to a crash between two trucks in Bedfordale.
The crash occurred on Albany Highway, near the intersection of Canning Dam Road just before 2pm.
The emergency rescue helicopter was unable to land at the crash site due to bad weather.
St John Ambulance is transporting two patients to Armadale Hospital.
Welshpool and Armadale Career Fire and Rescue Service and Armadale Volunteer Fire and Rescue Service firefighters helped free a person who was trapped.