South Yorkshire Police say both carriageways were closed, and the Yorkshire Air Ambulance has been reported on the scene.
Officers have just now re-opened the road.
A few minutes ago, South Yorkshire Police said: “The M18 has now re-opened in both directions between Junction 1 and 2 following an earlier police incident.
“Thank you for your patience and for avoiding the area whilst officers responded.”
It is understood the delays affected Sheffield United fans heading to Scunthorpe .