The collision took place on the A274 Biddenden Lane, at around 7.45am on Wednesday 18 July. It involved a white Ford Transit, a silver Skoda Fabia and a silver Suzuki Grand Vitara.
It occurred on a left band bend, close to Headcorn High Street.
The Transit was travelling in the direction of Headcorn and the other two vehicles were travelling in the opposite direction.
A man was taken to a London hospital for treatment to a serious leg injury.
A woman also sustained a leg injury and was taken to a local hospital.
Two other people sustained injuries which are not reported to be serious.
Officers from Kent Police’s Serious Collision Unit are investigating the circumstances and are keen to hear from anyone with information that is yet to speak with them.
They are particularly keen to obtain dash cam footage of the vehicles involved being driven, should any exist.