Police said on Tuesday they have arrested two men and a woman after finding what they believe to be components that could be used to make explosives in a flat in a Wong Tai Sin public housing estate.
Investigators said the three suspects, aged between 31 and 63, are from the same family.
They said officers found chemicals and laboratory equipment including measuring cups, electric cables, timers and heating devices inside the flat.
Police also raided a mini-storage space in San Po Kong that was rented by the 31-year-old man.
They said they found up to 15 kilograms of chemicals inside that could be used to make explosives.
"At the moment we're still trying to establish the quantity of explosives that could have been manufactured from the chemicals present," said Senior Bomb Disposal Officer Alick Bryce McWhirter.
"We are also working out whether the explosives were to be used in a single improvised explosive device, or IED, or home-made bomb, or to be used in multiple devices."
Investigators said they had traced the 31-year-old man from online comments that allegedly encouraged others to harass the police and members of the judiciary.