This dashcam footage from the United States shows a BMW 3 Series driver slam on the brakes, sparking a nasty pile-up.

Captured on a highway near the city of San Bruno, the video shows the driver of the E30-generation 3 Series hit the anchors hard (for seemingly no reason at all).

A Toyota Prius then crunches into the rear of the BMW, before an SUV slams into the back of the Prius.

Watch the footage above...