West Mercia Police said shortly before 5pm that it had closed the trunk road between the Dobbies and Emstrey roundabouts, with no access for vehicles to any roads on or off either junction.
Drivers were being advised to use an alternative route to avoid the closed road and the subsequent traffic.
West Mercia Police said: "Road closure for police incident, A5 from Dobbies roundabout to Emstrey roundabout, Shrewsbury. No access to any roads on or off the roundabouts either. Please use an alternative route."
An hour later, National Highways said the A5 was now open southbound, before police confirmed the road was fully open again shortly after 6.20pm.
At 6pm the AA's map showed long queues developing on numerous roads in the area, with traffic heading towards Shrewsbury queuing back past Preston Island on the A5, through Bayston Hill on the A49, Atcham on the B4380 and halfway towards Cross Houses on the A458.
Elsewhere, Thieves Lane and Oteley Road are reported to be very slow in both directions, as is Hereford Road between the Meole Brace and Dobbies roundabouts.
Queues heading east stretch back to Edgebold roundabout on the A5 and Copthorne Road on the B4380.