Emergency services were called to the scene in Chaucer Close at around 7.44pm on Wednesday after a vehicle crashed into the back of a lorry.
A male passenger was trapped inside the vehicle and had to be cut out of the car by fire and rescue teams from Copnor and Waterlooville.
A red fiat punto, which was carrying four young passengers, hit an Iveco dropside lorry that was parked at the side of the road.
An Alfa Romeo which was stationary at the side of the road was also involved in the incident as it was hit as a result of the crash.
No one was in either of the stationary vehicles at the time as they were both correctly parked.
The male driver and the two remaining female passengers escaped the crash with minor injuries after being treated at the scene and then later released.
The man was taken straight to Southampton General Hospital with serious head injuries.
Senior Investigating Officer Scott Davison said: 'At this stage we are trying to investigate the cause of the incident and the reasons why it happened.
'We would urge anybody in the area that saw it or saw the red fiat to come forward.'
Anyone with any information should contact Cosham police unit on 0845 045 45 45 quoting operation Samber.

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