A blue Ford Fiesta was travelling towards Kirkham when it collided with a Mini Cooper travelling in the opposite direction in Singleton Road.
The collision caused the Fiesta to flip before striking the perimeter fence of Weeton Barracks and a tree at around 4.55pm on Saturday (October 30).
The driver of the Fiesta - a man in his 20s - suffered injuries to his leg, chest, and head and was taken to hospital for treatment.
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Police said he was in a "critical but stable condition".
The driver of the Mini - a woman in her 50s - suffered "minor injuries"
Sgt Marc Glass, of the Lancashire Police TacOps team, said: "This was a serious collision which has left a man in hospital, and we are working hard to piece together exactly what occurred.
"We are now appealing for information and would like to hear from anybody who saw the incident, saw either of the vehicles in the moments before the collision, or who has dashcam showing either of the vehicles or any part of the incident.
"If you have any information, please get in touch straight away."
Anybody with information should call 101, quoting log number 1036 of October 30.
Information can also be reported online at doitonline.lancashire.police.uk.
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