The A46 is closed in both directions after an overturned lorry spilled syrup near Thorpe-on-the-Hill.
The road has been closed both directions between Newark Showground and Pennells Island Lincoln following the incident just before 11am.
The driver of the lorry was taken to hospital by air ambulance, and police are expecting major disruption on the road to continue late into the afternoon.
Highways England has said a large recovery and cleanup will be required, with motorists advised to allow additional travelling time or consider alternative routes if possible.
Drivers are being advised to travel to Lincoln via the Markham Moor junction, using the A57 before rejoining the A46 at Carholme Roundabout in Lincoln.