Officers hope that a local driver might hold the key to discovering what happened in the collision.
A 45 year old Preston women was hit by a Renault Megane on Deepdale Road this morning.
Police were called to the junction of St Thomas Road at 8:17am.
The woman, who suffered serious injuries to her leg and head, was rushed to Royal Preston Hospital.
The driver of the car, a 37 year old man, was unharmed in the collision.
Sgt Craig Booth, of Lancashire’s Tactical Operations Unit, said: “A woman is seriously injured and our thoughts are with her at this time."
"We are working to establish the circumstances of the collision and ask that anyone with information or any dash cam footage which may be relevant gets in touch.”
Anyone with information can call 101 quoting log number 232 of 13 June.