When Jackie was doing the stunt at the clock tower, he was afraid of falling voluntarily. So he held on until he literally lost his grip and fell.
Jackie Chan had no intention of making a sequel to this movie, but the Japanese Emperor enjoyed the movie so much, he told Chan he was looking forward to it, so Chan felt obligated.
Regarded as one of the most groundbreaking movies in Hong Kong Action cinema. Up to this point, Hong Kong movies didn't have the big scale sets and attention to period detail that was lavished on this movie. And it was the first to have a mixed variety of action sequences and not just rely on martial arts, which pretty much set the tone for the rest of Jackie Chan's movie career.
In rehearsal for the clock tower fall inspired by Safety Last! (1923), Chan took a week to build the courage to drop from such a great height. During the shooting of the bicycle chase sequence, one of the stuntmen informed Chan that E.T. the Extra-Terrestrial (1982) was playing at the local theater. Chan halted filming to watch the bicycle chase scene in the finale of E.T., to ensure that his scene and Steven Spielberg's scene were not the same. After watching the film, Chan became more confident, realizing that the audience doesn't really care so much about such minor details, only in watching the film and having a good time. According to his book I Am Jackie Chan: My Life in Action, Chan injured his neck while filming the scene.
The first Hong Kong movie where Jackie Chan opted for a more naturalistic, street fighting style rather than the traditional Kung Fu in his earlier movies.