The group were detained under the highly contentious new national security law, imposed by Beijing on the semi-autonomous territory last year.
News of the arrests came just an hour after Hong Kong’s chief executive Carrie Lam warned “ideologies” posed a threat to law and order and urged parents and teachers to report teenagers to the authorities if they are suspected of breaking the law.
According to the police, the nine alleged terrorists – aged between 15 and 39 – had planned to set off homemade bombs in courts, road tunnels, railways and rubbish bins in the street.
The group were allegedly caught trying to make the explosive TATP in a makeshift lab in a hostel and were found with the raw materials used to concoct the explosive and equipment.
TATP has been used in dozens of bombings around the world, including the 7/7 attacks in London, the 2015 Paris terrorist attacks and the Manchester Arena bombing. It is used by terrorists because it can be made from ingredients easily bought in shops.
Senior Superintendent Li Kwai-wah of the Hong Kong Police National Security Department said the nine alleged bombers were arrested on Tuesday.
The group hoped “to attack some of the public facilities in Hong Kong, including the Cross-Harbour Tunnel, railways, court rooms and they even wanted to lay bombs in the rubbish bin on the street, with a view to maximise the damage caused to the society”, he told reporters.
As well as bomb-making materials and manuals, police said they had also seized about HK$80,000 (about £7,500) and frozen a further HK$600,000 (about £56,000) in assets which they believe was linked to the plot.
If the police allegations are true, the bomb plot would be the most violent move yet by protesters opposed to China’s increasing sway over Hong Kong.
Since the national security law was brought in – in response to a mass pro-democracy movement which began in 2019 – the authorities in Hong Kong have used it to crack down widely on opposition.
Most prominent opponents of the pro-Beijing government in Hong Kong have either fled into exile overseas or been arrested. Most recently, a pro-democracy newspaper was forcibly shut down and several of its journalists, editors and executives arrested.
There have, however, been some violent attacks before among the otherwise mostly peaceful demonstrations. In 2019 the police arrested several people over alleged bomb plots and for making TATP.
And on 1 July this year, which marked the anniversary of Britain handing the territory back to China in 1997 and the Chinese Communist Party’s centenary, a man stabbed a policeman before killing himself.
Before the national security law banned such protests, the anniversary would be marked by large demonstrations against Beijing’s growing repression in Hong Kong. Now, any such demonstrators could be jailed for life if charged under the strict new law.
Police later said the attacker was a lone-wolf terrorist, based on unspecified material found on his computer.
Ms Lam strongly criticised Hong Kongers who came to the scene of the stabbing to lay flowers and pay their respects to the dead knifeman.
“They should not be wrongly influenced by the idea that ... breaking the law is in order, if you’re trying to achieve a certain cause," she said. “They should not be influenced into thinking that they can find excuses to inflict violence.”