Police have increased patrols on the MTR after receiving calls claiming toxic gas attacks would be made against passengers tonight.
Investigators are trying to establish whether the three calls to Wan Chai police station by a Putonghua-speaking man last Friday contain a credible threat.
Security Branch officials said there were adequate contingency plans which could be implemented within minutes of any disaster and urged the public to stay calm.
It is understood the calls, linked to the dispute over the sovereignty of the Diaoyu Islands, are being treated as 'most likely a hoax'.
But claims that the Aum Shinri Kyo doomsday cult, which unleashed sarin gas on the Tokyo subway system in March 1995, killing 11 people, were preparing to attack in Hong Kong would not be discounted.
Deputy Secretary for Security Alex Fong Chi-wai said: 'All those [government departments] who have a potential role to play are aware of the incident and they have been put on alert.
'Everybody is geared up to deal with any emergency that may arise. I stress that doesn't mean we believe it will arise.'