Esperance Police are still trying to piece together the events which resulted in his critical condition.

The man was brought into the Esperance Hospital by his friends on Saturday at about 4pm with serious head injuries and has fractured vertebrae and multiple fractures to the body.

It is believed he was riding in sand dunes on an off-road bike.

Officer in Charge Senior Sergeant Paul Humphries was concerned that the crash was not reported to the police on its occurrence.

“What we have now is a man with critical injuries but we don’t know how he sustained them,” he said.

Police are attempting to identify what took place.

“At this point we can only locate the mum and she is by his bedside in Perth.”

Police ask for anyone with information on the accident to call 9071 1900.