West Yorkshire Police have cordoned off the scene on Wyther Lane between B6157 Bridge Road and Broad Lane this afternoon.
A spokesperson for the force said someone had been assaulted on a bus.
The person has been taken to hospital and officers were sent to secure the scene.
The incident happened on a 49 bus heading from Bramley into Leeds.
The road was closed at approximately 3pm.
The police cordon stretches from Broad Lane up to the junction with the B6157
Bus detours are affecting 49 and 91 services and there are delays around the general area.
A spokesperson for First Bus, said: “We can confirm that a passenger on our 49 service bus in Leeds was attacked this afternoon and our driver acted swiftly in contacting the emergency services who have now closed the road.
"This was a serious incident and we will work closely with the police as part of their investigation, including providing access to our CCTV - which is fitted to all our buses in Leeds.”
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