The accident happened just before midday in Oakley, Hampshire. Ten ambulances were sent to the scene.
The two people who suffered life-threatening injuries and three others who were seriously hurt were taken to University Hospital Southampton for treatment.
Six people with minor injuries were taken to North Hampshire Hospital, in Basingstoke, along with three uninjured children who were not with adults at the time of the accident.
Seven other people escaped injury following the collision on the B3400 Andover Road.
The road is shut in both directions between the Dean Gate Pub and Oakley Village and the cordon is not expected to be lifted until this evening.
Motorists are being urged to avoid the area.