A senior criminal police commander warned on Wednesday about a surge in attacks from radical protesters — attacks he said smack of terrorism — as Hong Kong remains gripped by the social unrest that has plagued the city since mid-June.

This dangerous trend, aggravated by some people's reluctance to cooperate with police, has posed fresh challenges to the city's police force, said Tsang Chung-bun, assistant district commander for Yau Tsim district, Kowloon West Regional Headquarters.

Tsang cautioned members of the public to be alert to such attacks, before "any real catastrophe" happens. The veteran officer, with years of experience in criminal investigation, expressed concern over cases in which homemade bombs were found in a secondary school and residential areas, and of police arrests of criminal groups who had been testing explosives.

Tsang said the media and the public have downplayed the threat from the situation for political reasons. "Some reports even stressed that the source and purpose of the explosives were unknown; therefore they were not necessarily aimed at undermining public safety. Such remarks are irresponsible," Tsang said.

Criminal investigators like Tsang say that the frequent appearances of these dangerous items pose a great threat to Hong Kong's public safety — not only a "budding" threat, as some officials have claimed, but a substantial development of terrorism.

Tsang has been working on the front line since he joined the Hong Kong Police Force in 1995. He also offered his expertise in international cooperation to mainland police during his combined two-year stints in Beijing.