The first collision took place at around 3pm in Yarburgh Road, Covenham St Mary, when a blue Audi A6 left the road.
The driver, a man believed to be in his 50s, was sadly pronounced dead at the scene.
Less than three hours later, at around 5.50pm, the second fatal incident occurred in Louth Road, North Cockerington,
A grey BMW and a silver Ford Fiesta collided, and two people from the Fiesta were taken to hospital in Grimsby for treatment.
Tragically, a passenger in the Ford Fiesta, a woman believed to be in her 70s, died.
Anyone who was in the relevant area at the time of either collision, or who saw any of these vehicles prior to the collisions, is asked to contact Lincolnshire Police quoting incident number 196 (Covenham) or 241 (North Cockerington) of December 25.
Police would also be keen to hear from anyone who has dash-cam footage which could aid their investigations.