Detectives investigating the seizure of two powerful home-made bombs at a Hong Kong school campus believe they were intended for an attack on police at a massive anti-government march over the weekend, sources said on Tuesday. The apparent bomb plot, which emerged after six months of social unrest and political turmoil, prompted the city’s biggest police association to warn that the current security situation was at its “most alarming” in decades, even worse than during a wave of armed robberies in the 1990s. Superintendent Lau Siu-pong said on the official police Facebook page that more explosives and firearms could be similarly hidden across the city, and the two bombs were fully functional and primed to kill and maim. “We suspect that criminals temporarily stored the bombs there and intended to detonate them elsewhere,” Lau said. “Based on our intelligence and initial investigation, we believe it might not be an isolated case.” Police insiders told the Post the would-be bombers were forced to abandon the attack planned for Sunday after a group of their associates were arrested in a raid that morning, hours before the march – which attracted hundreds of thousands – started at Victoria Park in Causeway Bay. The bombs, packed with 5kg (11lb) each of high-grade explosives along with shrapnel in the form of nails, were not intended to target Wah Yan College Hong Kong in Wan Chai, where they were found, sources said. “The devices containing nails were designed to cause a lot of casualties in the attack,” one police source said. “We believe their target was police officers.” He added that intelligence indicated the gang had discussed in online conversations the use of explosives to attack police, and had used a flat, possibly in Wan Chai, as a bomb factory. The Sunday swoop happened at daybreak, police raiding three flats in Wan Chai, North Point and Chai Wan. They arrested 11 people and seized weapons including a pistol, 105 bullets, two bulletproof vests and some retractable batons. “The school is just five minutes away from the flat in Wan Chai that we raided on Sunday,” the source said. Officers suspected the gang, upon hearing of the raid, took the two bombs, hidden inside two black rubbish bags, to the slope under a Wah Yan College building. Someone claiming to be a school cleaner spotted the bombs under a building supported by pillars on a slope at about 5.30pm on Monday, though the force suspected he was really a rough sleeper. Bomb disposal officers later defused the devices. It was understood that the remote-controlled weapons – which officers said had a potential blast radius of up to 100 metres – would not have gone off on the slope, because two mobile phones connected to them, for use as detonators, were turned off. Another source said the chemicals used to make the explosives were difficult to get hold of, and police were investigating whether they had been stolen from local universities. He said officers were also investigating whether the Wan Chai bombs were linked with another device hidden in a flower pot in Mong Kok and detonated in October, soon after police officers moved in to clear protesters’ roadblocks nearby. No officers were injured in that explosion. The source added that the Mong Kok device – unlike those found at the school – contained highly volatile triacetone triperoxide, or TATP, and it was similarly controlled with a mobile phone. On Tuesday, officers were checking CCTV footage from along Queen’s Road East in Wan Chai and nearby areas, to gather evidence. ‘Deplorable’ petrol bomb attacks on Hong Kong courts condemned Lam Chi-wai, chairman of the Junior Police Officers’ Association, described the current security risk as the most “alarming” since the city’s return to Chinese rule in 1997, and even more worrying than during the armed-robbery epidemic of that decade. “I would have never thought of such security threats six months ago, when the anti-government protests began,” Lam said. “People are getting violent and audacious. Whatever people suggest on social media as ways to hurt police, some other person can make it happen. Now ordinary people could face bomb threats even when they go out.” Over the past six months, Hong Kong has been rocked by the anti-government movement sparked by a now-withdrawn extradition bill, with increasingly violent clashes between protesters and police. On Sunday, the Court of Final Appeal in Central and the High Court in Admiralty were firebombed during a mass rally , triggering alarm that radicals were starting to target the judiciary. Since June, police have arrested 6,022 people aged between 11 and 84 years over offences related to the protests, 2,392 of them students. Police also found more than 10,000 petrol bombs at several universities in November after protesters barricaded themselves on campuses and fought officers. Wah Yan College said there was no evidence linking the devices to any members of the school, as students sat their exams as scheduled on Tuesday morning. “The site where the bombs were uncovered belong to the school, but it is an open area outside the gates that can be accessed by the public,” the school said in a statement. So Ying-lun, an assistant school supervisor, said they had “not found any evidence pointing at teachers or students responsible for placing or making the bomb”, but the area the devices were found in was not covered by security cameras. A Form Six student surnamed Law said he passed by the area the bombs were found several times on Monday. “I was a bit worried because the bomb was placed right in the school,” he said. But Chan, 13, a Form One student who declined to give his full name, suspected the bomb could have been planted by outsiders as the campus sits on a hill surrounded by public roads. “I don’t think any of our students could do such a thing,” Chan said. A student in Form Three, who gave his name as Tsang, said he learned a bomb had been found on campus through social media on Monday night. “I was not too worried to go to school today, at least the bombs were removed.” he said. “I don’t think our students made them.” A father who was dropping his son off at school by car said a notice had been posted online last night assuring parents the school was safe. “It should be safe. I will also come to pick up my son after his exam,” the father, who gave his surname as Hon, said.