Shortly after 11:30 p.m., police responded to a two-vehicle crash in the area of Upper James Street and Inverness Avenue.
Police say a 31-year-old Hamilton man was stopped at a red light at the intersection when he was hit from behind.
He was taken to hospital with life-threatening injuries and remains in critical condition.
The driver of the other vehicle initially fled the scene but was later arrested, police said.
The collision reconstruction unit has taken over the investigation.
Police say speed and/or impairment have not been ruled out as factors in the crash.
Anyone with dash cam footage or information is asked to contact police at 905-546-4755 or Crime Stoppers anonymously at 1-800-222-8477.
