Flat Street: This incident is why police have closed busy Sheffield bus route today
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The man was found by British Transport Police officers at around 3am today near the junction of Flat Street and Pond Street, say police.
South Yorkshire Police officers have closed off the area and are carrying out further investigations to find out what happened.
It is not yet known whether the man was a victim of an assault or if he had suffered an accident of some sort.
He was taken to the Northern General Hospital from the scene for treatment to injuries.
Officers remain at the scene and are trying to find what happened.
Service 7 was scoming into Sheffield using Arundel Gate, Furnival Street, Brown Street, Paternoster Row into bus station then back on normal route.
The 120 was using Commercial Ctreet in both directions.