HONG KONG (Reuters) – The 50-year-old man who stabbed a Hong Kong policeman on the anniversary of the city’s return to Chinese rule on Thursday was a “lone wolf” who committed a terrorist act, Secretary for Security Chris Tang said.

Police said late on Thursday they were investigating an attempted murder and suicide after a man attacked a police officer from behind at 10.05 p.m. (1405 GMT), then stabbed himself in the chest with the knife.

The man was sent to the hospital, where he died about an hour later. The policeman, 28, sustained a 10 centimetres wound on his back and a punctured lung and underwent surgery, police said.

Speaking to reporters early on Friday, Tang said the stabbing was a “local lone wolf terrorist attack.”

He said police searched the home of the 50-year-old, whom he did not identify, and said materials on his computer showed he was “radicalised,” without providing further detail.

Security was tight in Hong Kong on Thursday, with thousands of police officers, as well as water cannon trucks and armoured vehicles deployed across the city.

The handover anniversary is when tens of thousands traditionally rally to protest anything from Beijing’s grip on the city to unaffordable housing. Police had banned gatherings this year, citing the coronavirus.

A national security law which Beijing imposed on Hong Kong last year in response to months of pro-democracy protests in 2019 has also discouraged people from gathering. The law punishes anything China deems as subversion, secession, terrorism and collusion with foreign forces.

More than a dozen people were arrested for “possession of an imitation firearm, possession of an offensive weapon, desecration of the national flag, distribution of seditious publications” and other offences, according to a government statement.

Hong Kong leader Carrie Lam, who had just returned from Beijing where she attended celebrations for the Chinese Communist Party’s centenary, condemned the stabbing and the other illegal acts in a statement.

“After going through months of riots in the second half of 2019, members of the public abhor violence and treasure very much the stability of society since the implementation of the National Security Law last year,” she said.

(Reporting by Jessie Pang and Donny Kwok; Writing by Marius Zaharia; Editing by Raju Gopalakrishnan)