Traffic was been diverted across St George Bridge, while officers deal with the incident, bus operators have said. It has now re-opened.
Bus operator First South Yorkshire said it was affecting its 41, 41a, 50, 50a, 50b, 51, 51a, 54, 64, 64a, 66, 09 and 412 services, which are also diverting, and the company apologised for inconvenience caused.
South Yorkshire Police have been approached for more information on the incident.