The collision, on Queensgate at the roundabout junction with St Chad Road, happened at about 11.15am today (Tuesday).
An 88 year-old man suffered "serious and potentially life-threatening injuries" in the crash involving a car, Humberside Police said.
The driver of the car failed to stop.
Witnesses reported the car to be a red Citroen Picasso, but police are yet to confirm the suspected vehicle involved.
Anyone with information is asked to call police on 101, quoting log 171 of January 16.