Police found the body of a woman inside a water tank at a residential building on Argyle Street in Ho Man Tin on Monday.
The victim was a security guard at the Mandarin Court building.
Police said they got a call from a guard working there at around 2pm, saying that his colleague was missing.
Officers found the body after a brief search.
Sources said the search was conducted after surveillance camera footage showed that the woman never left the building since starting her shift on Sunday morning.
A source also said police found a knife in the tank.