St George's Bridge is currently closed in both directions with and queuing traffic into town between St Mary's Roundabout and Markets Roundabout as a result of the incident.
A South Yorkshire Police spokesman said: "Police are currently in the St George’s Bridge area of the A19, Doncaster, responding to concerns for the safety of a woman at that location.
"Surrounding roads are closed while emergency services respond and motorists are advised to plan alternative routes."
A diversion is in operation via St Mary's Bridge, and there is also congestion on A638 York Road to the A635 Barnsley Road junction and on A19 Bentley Road to the Cusworth Road junction.
More to follow.