The collision occurred at the junction of York Road and Sprotbrough Road at around 6am today and has led to the closure of York Road from St Mary's roundabout to the junctions with Pipering Lane and Stanley Road.
Some buses were diverted along Sprotbrough Road, onto Spring Lane, Long Lane and Cusworth Lane earlier but now the town is said to be gridlocked because of road closures and a build up of traffic as motorists try to avoid the crash scene.
The number 66 Bentley service and 64a Arksey service have been suspended.
Services 41, 41a, 50, 50a, 51, 51a, 54 and 66 are running 90 minutes late as the outbound services operate out of town via Balby Road and the A1M.
Inbound services are unaffected.
A number of police vehicles and ambulances were at the scene earlier
Firefighters alerted to the smash at 6.06am cut one casualty free from a vehicle involved.
No other details on the nature of the crash have been revealed.