According to Lincolnshire Police, the motorcycle crashed at about 4.30pm this afternoon (Friday).
Duty Inspector Gordon Richard said the male rider is not thought to be as seriously injured as first thought.
He said: “The road is closed while investigations are ongoing. There are diversions in place as the road is closed between Holdingham roundabout and the Quarrington roundabout for the A153.”
He could not say how long the road would be closed for but at least an hour.
Vehicles were being turned away with diverted traffic causing congestion and tailbacks through the town centre.