The A16 remains closed at Cowbit this lunchtime.
Lincolnshire Police originally said two vehicles were involved in the incident but that has now increased to four.
A person has been taken to hospital with serious injuries.
The road has been closed between the A1175/B1173 (Applegreen Roundabout) to B1357 Moulton Chapel Road (Cowbit Roundabout).
Police are not disclosing which types of vehicles are involved at this time.
The incident was first reported at around 5.30am this morning (Wednesday).
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