Bystanders desperately tried to save a fatally injured dirt bike rider in the moments after they crashed at a motorbike park yesterday.

Emergency services were called to the single-vehicle smash at the Helensville park around 2.15pm, a police statement said.

"Members of the public had attempted to render medical attention but the rider sadly died at the scene."

The Serious Crash Unit attended the scene along Rimmer Rd and WorkSafe has been advised.