Riot officers, who raised a red flag warning people to stop charging, said protesters had been shining laser pointers at them.
After the first batch of pepper spray was fired, angry protesters began kicking water barriers in front of the riot officers. More pepper sprayed was then unleashed, hitting an RTHK reporter.
Meanwhile, people were still streaming into Tamar Park for the two-hour rally from 7pm organised by the Civil Human Rights Front.
Thousands were already gathered there for the demonstration to mark the fifth anniversary of the start of the Occupy movement.
In light of the confrontations, organisers urged people not to enter the park via the bridge linking Admiralty Centre to the government’s headquarters, warning they risked getting caught up in clashes with the police.
The Legislative Council building next to the park was also in lockdown mode, with a “red alert” issued due to the rally.