The A47 is currently closed between Swaffham and Lynn after a collision involving a car and a lorry at East Winch.
Emergency crews were called to the incident at around 12.20pm, and are still on the scene.
Motorists are being advised to avoid the area if possible.
A police spokeswoman said a man was being treated by paramedics, but the extent of his injuries were unkown at this time.
She said there were also reports that someone had been trapped in their vehicle.
A post on the King’s Lynn Police Twitter account at 1.25pm said: “A47 currently closed between Swaffham and Kings Lynn due to an RTC, road closed for several hours, please avoid the area if poss.”