Police said they have arrested a 20-year-old woman in Kowloon district for violating assembly laws in the early hours of Monday. Since the protester had a head injury, the officers called for an ambulance truck to pick her up and drive to a hospital (the police did not specify how she was injured).

The truck did not get far, however, as around 3am local time it was stopped and swarmed by hundreds of protesters, who hurled rocks and bricks at the two escorting officers hiding behind the seats inside the vehicle, while also splashing “unknown liquid” on them.

The protesters then began rocking the ambulance truck. That’s when one of the officers fired three warning shots, dispersing the rioters. “Initial enquiry shows that the shots did not hit anyone,” police said. The arrested woman managed to flee and is now on the police ‘wanted’ list.

Battles between the authorities and protesters intensified over the weekend, when the police attempted to remove the barricades erected at the Hong Kong Polytechnic University (PolyU). Large fires broke out outside the campus when rioters hurled petrol bombs at law enforcement.

On Monday, CNN published a photo, taken at the PolyU, of what appears to be a homemade explosive device – a large gas canister rigged with dozens of bolts. The channel could not independently verify whether it was actually a bomb, but police told them the protesters have used gas canisters against them in the past.