The A15 has been closed between the A1500 Tillbridge Lane and the A631 Caenby Corner due to a serious three-car collision.
One man has been taken to Hull Royal Infirmary by air ambulance.
Police say the road is expected to be closed for a few hours.
The crash happened at around 4.45pm on Monday, May 21.
The vehicles involved are a blue BMW, a silver Mercedes-Benz lorry and a silver Land Rover.
A Lincolnshire Police spokesperson said: “We are appealing for anyone who was travelling on the A15 around that time and may have seen any of the vehicles mentioned travelling in the area or who saw the collision itself to call us.
“We would also appreciate anyone who thinks they may have dashcam footage of the vehicles to get in touch.
“We will release further details when we are in a position to do so.”
Anyone with information can call Lincolnshire Police on the non-emergency 101 number.