Due to the severe weather conditions the A35 Puddletown bypass has been closed both ways between Bere Regis and the Stinsford roundabout at Dorchester.
Around 100 vehicles are currently believed to be stuck on the road and officers are reassuring those involved that the emergency services and other agencies are doing all they can to assist.
Chief Inspector Alan Setchell, of Dorset Police, said: “We want to get a message to all those involved to reassure them that we are fully aware of the situation and the emergency services and partner agencies are making every effort to assist everyone as quick as they can.
“I would make a special plea to anyone who has a particular urgent medical need or requires immediate assistance to contact us on 101 and give us your precise location so we can assist you as a priority.
“People are urged to stay in their vehicles and we will get to you as soon as possible.
“We have a number of major routes and other roads affected by the severe weather around the county and I would urge members of the public to avoid travelling if it is at all possible.”