Hong Kong has had an horrific reminder of its vulnerability to violation of public safety, whether random acts of inhuman violence or terrorism-related. The lessons must be learned and rigorously applied. But our first thoughts, and our prayers for their full recovery physically and mentally, must be with the victims of Friday night’s firebombing of a peak-hour MTR train at Tsim Sha Tsui. It is testament to the shocking nature of the incident that witnesses who were unhurt but traumatised by what they saw must also be considered victims. They too may need post-stress care.

The incident does not signal Hong Kong’s loss of innocence to terrorism. The health chief has confirmed that the alleged perpetrator, who remains among those in hospital, has a history of mental illness and, though relatively stable of late, had missed a recent medical appointment, after which medics could not contact him. This is not an unusual occurrence among such patients, but it calls for an urgent review of whether there are more effective ways to ensure treatment reaches those who need it to maintain behavioural stability, for their sake and that of their loved ones, carers and the general public.

That said, the incident sounds a resounding public security alert, if not a full-scale terrorism alarm, for the whole city. The MTR, of course, remains the prime concern with subterranean operations that move millions of passengers a day. But it would be a false sense of security for either the authorities or the general public not to recognise that Hong Kong’s reputation as one of the world’s safest cities is facing a challenge in a year of high-profile events associated with the 20th anniversary of the return of the city to China. Potential threats are not confined internally to people with grievances or psychological issues. As an open city with freedom of movement we cannot assume we are invulnerable to the kind of terrorist atrocities visited on European cities in recent times. There is a need for balance to safeguard our cherished liberties, but security officials must redouble their vigilance, and the authorities should consider the need for advice for the public to follow in future incidents.