Hong Kong police found 14kg of dangerous substances and an improvised bomb at an abandoned school in eastern Kowloon on Saturday, with a senior officer saying some of the chemicals appeared to be from the campus of Polytechnic University occupied by protesters last year. The disused site on Choi Shek Road in Ngau Tau Kok had been used by officers in the past to carry out exercises, but none of those drills involved such materials, the police said. The discovery is the 11th bomb case the force has handled since anti-government demonstrations broke out last summer and comes after a 60 per cent jump in the number of cases involving explosives in 2019 over the previous year. Four people playing war games at St Joseph’s Anglo-Chinese School found the suspicious objects in the male washroom on the ground floor and alerted police at around 1.30pm. Officers from the explosive ordnance disposal bureau arrived and roads around the area were cordoned off. They found about 10kg of chemicals and roughly 4kg of finished explosive substances, as well as the improvised explosive device, modified mobile phones, circuit boards and a pressure cooker. “We are very, very worried,” said Senior Superintendent Steve Li Kwai-wah of the organised crime and triad bureau, noting pressure cookers were often used in terror attacks. “If these items still remain in the community, maybe it will cause a greater threat to social security.” The police had not determined the power of the explosives but said the items were stable and no detonation was carried out at the school. IED found at border point, after another suspected toilet bomb But cyanide and chloroform – toxic and highly flammable – were among the chemicals seized. “Making a comparison to the shape and packaging of some lost items reported, I believe they are linked to the lost items from Polytechnic University last November,” Li said. The university was one of several students took over at the height of violence during the anti-government movement sparked by a now-withdrawn extradition bill. Campuses became war zones as a core band of protesters armed with petrol bombs, bows and arrows and even rudimentary catapults faced off against riot police equipped with rubber bullets, tear gas and water cannons. During a nearly two week siege at PolyU, the university reported that chemicals were missing from their laboratories. The police classified the latest cases as suspicious object found and no arrests had been made. Anyone found guilty of possessing and making bombs can be jailed for up to 14 years. The city has recorded an increasing number of bomb cases in recent months. Last year, police handled nearly 190 cases – 60 per cent more than the year before. In early March, authorities seized more than two tonnes of explosives and chemicals , arresting 17 people accused of plotting attacks against police officers. In January, a palm-sized device was discovered in a rubbish bin at the Shenzhen Bay Control Point, just 12 hours after a public toilet in West Kowloon was set ablaze by a suspected home-made bomb. A bomb was also found in a toilet at the Caritas Medical Centre in Cheung Sha Wan the same month. Help us understand what you are interested in so that we can improve SCMP and provide a better experience for you. We would like to invite you to take this five-minute survey on how you engage with SCMP and the news.