Yuta Sugimoto, 20, was arrested Monday with another man for allegedly confining a woman in her car for a few hours, robbing her and sexually assaulting her.
Sugimoto escaped from the interrogation room of the public prosecutor's office at 2:15 p.m. Tuesday.
Police said they have tightened security at schools in Kawasaki and placed him on the national wanted list.
Four-thousand officers are looking for the man, using 900 patrol cars, helicopters and boats, Kyodo News reported.
Sugimoto is described as 5-foot-4 and weighing 141 pounds. During questioning, he was wearing a white sweatshirt and navy blue sweatpants but police speculate he changed clothes while on the run.