Volunteers at Shek Kip Mei Park said CCTV showed a man putting something into two food bowls for stray cats in the early hours of October 24. They stopped him and called police; officers arrested a 34-year-old man on suspicion of animal cruelty and possession of an offensive weapon.
The volunteer group Hong Kong Suspected Animal Abuse Report said the bowls also contained black sludge-like material.
Footage supplied by a group representative showed a man opening a packet and pouring its contents into a bowl on October 18.
Police said they found a packet of suspected rat poison and a fruit knife on the man, who was being detained for investigation. They said no cats were injured.