Police have arrested a man following an alleged hit-and-run crash in Adelaide's northern suburbs, but he is refusing to say if he was the driver involved or not.

Emergency services were called to the corner of Bridge and Ayfield roads at Para Hills West just after 12:00pm after a 21-year-old Ridgehaven motorcyclist was critically injured in a collision with a car.

Police say the red or maroon 1999 Holden Vectra sedan involved in the crash allegedly drove off, heading south, before police arrived.

It was located about 4:30pm in Peacock Road, Para Hills West.

Major Crash officers investigating the incident charged a 50-year-old man from Para Hills West with failing to truly answer questions in relation to who the driver of the vehicle was at the time of the crash.

He has been refused police bail and is expected to appear in Elizabeth Magistrates Court on Monday.

Bridge Road has reopened to traffic.

The rider was taken by ambulance to the Royal Adelaide Hospital.