Spridlington Road has been closed in both directions at Faldingworth after a motorbike left the road.
Police said the biker has sustained serious injuries in the crash, which happened at around 11am on Thursday, March 24.
The road has been closed from the Snarford turnoff to the Newtoft turnoff. A police cordon is expected to be in place for around two hours.
Lincolnshire Police asked drivers to avoid the area.