A motorcyclist has captured some seriously bad behaviour on one of Perth's major freeways on camera, and says the footage should be a strong message to other riders about staying safe on the state's roads.

Mark Smith was driving on the northbound stretch of the Mitchell freeway near Whitfords at about 4.45pm on Tuesday when he spotted the car erratically overtaking drivers in the right hand lane.

"As a motorbike rider on Perth's roads for over 30 years, I thought I'd seen it all, but then I came across this one yesterday," he wrote.

The video captures the driver overtaking Mr Smith in the narrow emergency lane, before speeding up and tailgating a second driver.