Hong Kong’s cherished reputation as a safe, law-abiding place remains largely undiminished, despite extraordinary events like Occupy Central and the more recent firebombing of an MTR train by a man with a history of mental illness. But the risk of loss of innocence in the age of terrorism remains ever-present, if not inevitable. The abiding fear of security authorities is that the agent of it will be an individual radicalised by Islamic State (IS), who may be already living in the city. Such lone-wolf attackers are among the hardest to stop. The anti-terrorist police are on alert to prevent them, even though the terrorist threat level remains moderate. Police insist the danger is real, as evidenced by deadly suicide bomber attacks on Brussels and Istanbul airports last year. This is one reason the elite airport security unit conducts regular emergency drills with airlines and Hong Kong airport shops.

The warning came as security experts called on the authorities to raise public awareness of global terrorism so as to recruit more “eyes and ears” to look out for unusual or suspicious activity. Less than two months ahead of the expected visit of President Xi Jinping and other state leaders for the 20th anniversary of the handover, it is hard to see such a warning as just a coincidence. The heavily weaponised security for the recent visits by Indonesian President Jokowi Widodo and Philippine President Rodrigo Duterte were fortuitous dress rehearsals for Xi’s visit. Extremists are known to choose occasions that attract crowds to unleash their violence. The 20th anniversary of the handover and the swearing in of a new chief executive make July 1 an ideal time to send a political message.

Police may not have concrete evidence of a threat but believe it foolish to rule it out.