The street sweeper and a small car crashed head-on near Cerritos and Knott avenues at about 2:30 a.m., according to William Mattern of the Orange County Fire Authority.
The driver of the smaller vehicle was pronounced dead at the scene, and the driver of the street sweeper was transported to UCI Medical Center as a critical trauma patient, Mattern said.
The Orange County Sheriff's Department was investigating the cause of the crash.
Meantime, Cerritos Avenue was closed between Knott and Western avenues until further notice.