Police have closed part of Foundry Approach in Harehills while emergency services work at the scene.
A spokeswoman said officers had been called shortly before 7am to a collision near the junction with Broughton Avenue.
She said a man in his 20s has been seriously after the crash involving a silver Toyota and a black Suzuki motorbike.
First Bus has said its number 4 and 16 services are being affected by the disruption on Foundry Approach.
The services are diverting via Harehills Lane, Strathmore Drive, Foundry Drive and Foundry Avenue in both directions.