Transport minister Eva Cheng and pro-government legislators were trapped inside the Legislative Council building until early today, with several hundred hardcore protesters blocking all the exits.
The crowd - which peaked at 10,000 according to organisers and 1,700 according to the police - was boosted by thousands of mostly young onlookers keen to sample the almost festive atmosphere which had been building in Statue Square since Thursday.
But all carnivals must leave town, and early today units of riot police moved into position, seemingly to take protesters away.
Just before 6pm, as the vote to approve funding for the rail line dragged to its inevitable conclusion, a hardcore group began wrapping their faces with plastic wrap to minimise the effect of pepper spray; others used hoods and bandanas, while one even wore a mask like that sported by the hero in the 2005 movie V for Vendetta, about a freedom fighter who uses terrorist tactics to fight a totalitarian society.
A first attempt by a few dozen to storm the building was blocked by rows of police. By 6.10pm, with chants of 'shameful government, shameful pro-establishment and shameful functional constituency' reaching a crescendo, large groups began trying to find other ways into the building.
Scuffles broke out with police as protesters attempted to break through the metal barricades brought in to keep them out. Some briefly breached police lines; others were arrested. A phalanx of police surrounding the building began using pepper spray.
At 7pm, the protesters began calling for everyone to block all the exits to the buildings. Nevertheless, at about 7.15pm the minister and other officials attempted to leave by minibus along Jackson Road.