The A45 is closed westbound from the near Rushden Lakes to Turnells Mill Lane in Wellingborough.
A police spokesman said the accident was a three vehicle collision that was reported to police at 10.30am this morning.
Police, fire and ambulance services are all on the scene and the road is likely to be shut for some time.
PC Lee from the Safer Roads team said on Twitter that police are working to turn around vehicles trapped within the road closure between Rushden Lakes and Wellingborough.
Traffic England shows vehicles are not moving on the road and traffic is extending beyond the road closure.
One driver, Si Vert, said: "You can't get to Wellingborough or Northampton on this route. It took me 1 hr 36 mins to get from Irthlingborough to Northampton after being diverted from A45 Westbound, past Waitrose and up Ditchford."