City Under Siege (simplified Chinese: 全城戒备; traditional Chinese: 全城戒備 is a 2010 Hong Kong science fiction action film directed and co-written by Benny Chan. The film follows a group of circus performers who goes on a rampage after an accidental exposure to chemical gas left by the Japanese army in World War II, granting them superhuman abilities.

Plot

Sunny is the orphaned child of a former knife throwing master. After his father's death, he is taken in by his uncle, who allows him to perform as a clown, due to the fact that he has not apparently inherited the skills of his father; nevertheless, Sunny still has the wish to perform knife throwing. He is ridiculed and tormented by the children of his uncle, who are all skilled performers in his uncle's troupe. One day, Sunny stumbles upon the plan of the rest of the troupe to explore a cave rumored to be filled with gold. Instead of killing Sunny, they decide to use him as point for their exploration of the cave. They find crates filled with capsules, and force Sunny to open them. Inside the first are numerous plates of gold. They then try to kill Sunny, and continue opening the rest of the capsules. These contain experimental gas which transform them into superhuman monsters.