Highways Englandt said the A1 is closed in both directions between the A43 near Stamford and the A47 near Wansford due to a serious collision.
Cambridgeshire Police and Emergency Services are in attendance and diversion routes are in place.
Cambridgeshire Police said on social media: ‘Please avoid the A1 between the A43 and Carpenter’s Lodge, road closed, police at the scene.
Road users traveling south are advised to follow the hollow triangle detour symbol on traffic signs
Leave the A1 at the A43 Worthorpe junction and turn right south onto the A43.
Continue on the A43 through the villages of Easton on the Hill and Colleyweston.
At the A43/A47 Duddington roundabout, turn left east onto the A47. Continue on the A47 to the Wansford interchange.
Pass the first roundabout (north entrance of the A1) cross the bridge and turn left at the second roundabout.
Follow the ramp onto the A1 heading south.
Road users traveling north are advised to follow the Hollow Diamond detour symbol on road signs
Leave the A1 at the A47 Wansford junction. At the top of the ramp, turn right west on the A47.
Continue on the A47 to the A47/A43 Duddington roundabout. At Duddington roundabout turn right north onto the A43.
Continue north along the A43 through the villages of Colleyweston and Easton on the Hill.
Take the first left at the A43/A1 junction, the northbound slip road and join the A1.
If this closure impacts your planned itinerary, please allow additional travel time. Plan ahead, you might want to change your itinerary or even delay your trip.