Officers and police vehicles are barring entry to Silver Street today (July 4) and have reportedly been on the scene since around 4am.
Closures are also in place on High Street, Scot Lane, Hall Gate and Printing Office Street to keep motorists out of the one-way traffic system.
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A single police car also appears to be guarding a small scene in Wood Street, near to what what looks like the snapped off top of a wooden door lying in the road.
Silver Street is home to much of Doncaster’s nightlife venues, and the cordon takes in several city centre bars and pubs.
Traffic is heavier than usual in surrounding streets because of the closures, particularly on nearby Thorne Road and South Parade.
South Yorkshire Police has been contacted for a comment.