Emergency services rushed to the A16 at North Thoresby following a three-vehicle collision.
The collision involved a Volkswagen Tiguan, a Ford Focus and a Nissan Navara.
A 75 year-old man from Louth, who was driving the Focus, was taken to hospital with serious injuries.
Two other casualties from the collision were treated in hospital for less serious injuries.
The collision occurred shortly before 3pm at the junction with White Road, and involves three vehicles.