A teenager was flown to a paediatric major trauma centre following an incident involving two cars in East Haddon.
Eyewitnesses said the incident happened on the A428 at the East Haddon crossroads on Saturday (September 8).
A spokesman for the Warwickshire and Northamptonshire Air Ambulance said: "The Derbyshire, Leicestershire & Rutland Air Ambulance responded to a call at 4.45pm on Saturday 8 September and arrived on scene in East Haddon, Northamptonshire at 5.02pm.
"The crew attended a road traffic collision involving two vehicles. There were four seriously injured patients and a teenage male was treated at the scene before being flown to a paediatric major trauma centre."