Sherman Police Chief Joel Spellins said the fire is contained to the southbound lane and they are diverting southbound traffic onto the old Highway 9.
The Mississippi Highway Patrol is working along with local fire departments to extinguish the hay, truck and trailer.
The fire is in patches along a quarter of a mile stretch between Endville and Cochran roads.
Spellins said traffic is flowing but it is being diverted onto the old two-lane highway.
Northbound traffic isn't affected.