Emergency services were called to the scene just before 7pm.
Officers from Hampshire Roads Policing from Whitchurch closed the road following the collision involving a Citroen, Mitsubishi Outlander, and a Jaguar near to The Strave on the outskirts of Four Marks Village.
Hampshire Fire and Rescue service sent crews from nearby Alton, Winchester and Alresford. It is understood that crews removed the roof of the Mitsubishi using specialist cutting equipment to release the family who were trapped in the vehicle following the horrific collision on the 30 mile an hour stretch of road. South Central ambulance also attended the incident.
Police have advised that the road is likely to be closed for a number of hours well into the early hours of Monday morning for Collision scene reconstruction and a clean of the road. Specialist recovery contractors JD Motors have been called in by Police collision examiners to help with their investigations.
A Hampshire police spokesman said
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.