A woman is in a critical condition in hospital after she was struck by a marked police van responding to a 999 call.
The pedestrian was on the B1135 Wymondham Road in Hethel, about eight miles south-west of Norwich, when she was hit at around 10.20pm on Thursday, Norfolk Police said.
The woman was taken to Addenbrooke's Hospital in Cambridge by air ambulance in a critical condition.
Nobody else was injured.
A Norfolk Police spokesman said: "Officers were in the area responding to a 999 call relating to concerns for the safety of a woman who had been reported missing.
"The road was closed while initial scene investigations were carried out and remains closed this morning.
"In accordance with normal procedure, Norfolk Police has referred the matter to the Independent Police Complaints Commission."