The subversives in Hong Kong have stepped up their crusade to paralyze the city with a "blossom everywhere" campaign of violence and vandalism across the city.

That flowery phrase hides the malice driving their actions.

Acts such as firebombing the inside of subway trains with passengers on board; throwing objects onto rail tracks to stop running trains; dropping sharp or heavy objects on moving vehicles from overhead walkways; setting fires inside road tunnels; throwing Molotov cocktails at buses loaded with passengers, including school pupils and elderly people; beating up drivers and passengers who try to remove roadblocks; and even dousing a man with a flammable liquid and setting him ablaze demonstrate the rioters have lost both their humanity and reason.

The violent hysteria of the troublemakers has brought the city to "the brink of total collapse", the police have warned, with their "insanity" forcing schools and shopping malls to close, as well as forcing the shutdown of large parts of the transport network.

Hong Kong's Education Bureau suspended classes at primary and secondary schools on Thursday because of the risks posed to children's safety, describing the situation in the city as "chilling". It called for schoolchildren to stay at home, "and not to participate in illegal activities".

Many of the masked people taking part in the protests are thought to be high school and university students. And these self-styled urban guerrillas have sought to turn Hong Kong's three university campuses into "revolutionary bases" from where they can launch their attacks on nearby traffic and transport arteries.

A social media post widely circulated among protester groups called for reinforcements to rally to the university campuses, saying the campuses are the "most important battlegrounds, which must not be lost".

It is not that these self-anointed rebels have any love for these seats of learning. They merely consider the campuses safe havens from police enforcement actions because of an established practice that requires police officers to notify the school management before they enter a campus to execute their duty.

This is a courtesy that should no longer be practiced given that under the Public Order Ordinance, police can enter any premises, with reasonable force if necessary, to stop or disperse a public gathering, other than a religious one, if they reasonably believe it could cause or lead to a breach of the peace.

"Nowhere in Hong Kong is lawless land," a police spokesman said, explaining the police had raided Chinese University of Hong Kong, because it was being used as a factory to make gasoline bombs.

The black-clad rioters need to be reminded: Campuses can never be safe havens for criminals.