“Dear world … Be aware or be next”: Those chilling words are the literal writing on the wall at the Hong Kong Polytechnic University, where roughly 600 pro-democracy protesters are locked in a violent standoff with police.

For days, the protesters have managed to ward off cops, using bricks, slingshots, bows and arrows and homemade firebombs to keep them from entering the campus. The police, in turn, cordoned off all escape routes, demanding the protesters surrender or meet tear gas and rubber bullets. At least 38 have been injured, and dozens more arrested.

The clash at PolyU marked the second time Hong Kong police have stormed a university, claiming schools are used as weapons factories. Carrie Lam, the city’s Beijing-chosen chief executive, calls the university protesters “rioters,” blaming them for raising “the level of violence.”

But the protests, which began in June over a bill to make Hong Kongers subject to extradition to mainland kangaroo courts, were peaceful until police turned up the aggression. And it’s the cops who are now preventing the protesters from fleeing the campus peacefully.

This is how Beijing is keeping its vow (and treaty obligation) to respect Hong Kong’s liberties until at least 2047.