The accident took place when the BMW vehicle was in a rehearsal, along with its convoy on the NH-37, Guwahati Deputy Commissioner of Police (Traffic) Pranabjyoti Goswami told PTI.
"During the exercise, the car hit another vehicle in front of it in the convoy," he said.
Nobody was injured in the incident, but the steel frame of BMW's front grill and its bonnet were damaged under the impact of the collision.
Asked if a replacement car will be brought in, he said it depends on the decision of the Prime Minister's special security team, that will assess the damage.
Prime Minister Narendra Modi along with a host of other high-profile dignitaries, including union ministers and many chief ministers, will attend the swearing-in of Sonowal here tomorrow.