WorkSafe is investigating a collision between a four-wheel-drive and a quad bike last week that left a 25-year-old man critically injured.

The collision took place on private property at Scott River East last Thursday afternoon. It is believed visibility in the area may have been reduced by smoke.

The quad bike rider was a 25-year-old man who was airlifted to Perth and remains in a critical but stable condition.

Inspectors have travelled to the site and, in cooperation with WA Police, will investigate the circumstances.

WorkSafe thoroughly investigates serious work-related injuries and deaths in WA with a view to preventing future incidents of a similar nature.