A man suffered serious head and pelvis injuries after being involved in a collision with a car in Preston, police said.
The pedestrian, believed to be 26, was taken to hospital after the crash, which happened on the bend in Mariners Way, close to Morrisons, at around 7.35pm.
Police are now hunting the driver of a black car, believed to be a Volkswagen, that failed to stop at the scene.
One worker at a nearby business said officers had already made enquiries about the firm's CCTV footage as their investigation got underway.
A spokesman for Lancashire Police said the county's Roads Policing Unit (RPU) was leading the enquiry, and said officers had initially been called in by the ambulance service.
Information can be reported to police by calling 101, quoting log number 1337 of Saturday, February 18.