The crash happened at the junction of Hornchurch Road and Abbs Cross Lane
The 43-year-old rider was injured in the crash near Harrow Lodge Park early this morning.
He is in hospital and his family has been informed.
It happened at the junction of Hornchurch Road and Abbs Cross Lane at around 12.35am.
The driver of the bus, an N365, stopped at the scene and police say no arrests have been made.
Detectives from the Roads and Transport Policing Command are investigating and would like to speak with anyone who saw the collision, or the moments leading up to it, or who captured it on dash cam.
Anyone with information is asked to call the Serious Collision Investigation Unit on 020 8597 4874 or via 101 quoting reference Cad 271/08Dec.?
Tags: Havering, Hornchurch