Officers are appealing for information following a serious road traffic collision on the A31 at Four Marks.
The incident happened at around 6.35pm on Sunday, 5 November and involved a Mitsubishi Outlander, a Citroen C1 and a Jaguar XE.
Five people were injured in the collision.
The driver of the Mitsubishi Outlander, a 70-year-old man, received minor injuries. The passenger, a 72-year-old woman, suffered serious injuries.
The 66-year-old woman who was driving the Citroen C1 sustained life threatening injuries. The passenger, a 49-year-old woman, received serious injuries.
All four people were taken to Southampton General Hospital for treatment.
The driver of the Jaguar XE, a 56-year-old man, suffered minor injuries and was treated at the scene.
Sergeant Andy Noble of Hampshire Constabulary’s Roads Policing Unit said, "I am appealing for anyone with information about this incident to get in touch.
“A number of people have been seriously injured and the road was closed for more than four hours while we dealt with this incident.
“I would ask anyone who witnessed this collision or anyone who has any information that could assist our investigation, to contact us."
If you have any information relating to this case, please call 101 quoting reference '44170431554', or contact Crimestoppers anonymously.