Police officers, four fire crews, and six paramedic crews from across the area were called just before 8pm to reports of a collision involving a grey BMW and a silver Volkswagen Golf on the A32, by the Cott Street junction, near Swanmore.
All three occupants of the vehicles – two women and one man – suffered serious injuries, according to Cosham firefighter Nigel Blackman.
He said: ‘The collision appeared to be head-on.
‘It involved two females and one male, all extracted by us and taken to hospital by the South Central Ambulance Service.’
All three individuals were taken to Southampton General Hospital, where the passenger of the BMW, a 20-year-old woman from Hook, died yesterday evening.
Her family has been informed and are being support by specialist officers, according to a spokesman from Hampshire Constabulary.
He said: ‘Enquiries are being conducted into the exact cause of the collision, and we are keen to speak to anyone with information.
‘Were you in the area at the time? Perhaps you saw a grey BMW or silver Volkswagen in the run up to the collision or maybe you have dash-cam footage?’
Anyone with information can make contact online or by calling 101 quoting Operation Zircon or reference number 44210043645.
Alternatively, you can contact Crimestoppers online or by calling anonymously on 0800 555 111.