In a rare show of dissent, 13,000 civil servants filled Chater Garden in the heart of Hong Kong's business district last night to protest against the government's handling of a contentious extradition Bill.

The park was filled to the brim, with many standing on grass patches and among shrubs, and thousands more spilling out onto surrounding roads. Hundreds more were perched on the roofs of a surrounding shelter while others had to watch from a nearby flyover.

As an evening shower set in, the area was turned into a sea of umbrellas. Legislators, former senior civil servants and trade union representatives gave speeches in support of the anti-extradition movement. They included former government No. 2 Anson Chan, who called on the government to examine why its employees saw the need to speak up.

The official in charge of the more than 170,000 civil servants in Hong Kong had warned them not to join the protest movement. "Doing so would shake the public's confidence that civil servants can remain politically neutral and carry out their duties in an impartial manner," said Secretary for the Civil Service Joshua Law in a letter on Thursday.

Most participants said they had come after work and many wore masks for fear of being identified.

"It's very sad to see the government this way because we are supposed to serve the city. Coming out tonight is the least I can do to support the movement," said Ms Ella Yu, who is in her 20s. She declined to say which department she worked in.

Hong Kong has for weeks been rocked by a series of protests and acts of civil disobedience after the government attempted to rush the extradition Bill through the legislature. If passed, it would have allowed for the transfer of fugitives to several jurisdictions, including mainland China.

Millions marched on the streets for two weekends in June against the Bill, forcing Chief Executive Carrie Lam to declare that the proposed legislation was "dead" and indefinitely shelved.

But that has done little to placate opponents, who are demanding that Mrs Lam formally withdraw the Bill. Anger has also shifted to the police, whom many have accused of using excessive force to disperse protesters. The protests have also shifted towards calling for democratic reforms.

Rallies over recent weekends had started peacefully but degenerated into violence as groups of protesters stayed behind in a stand-off with the police. But yesterday, attendees peacefully left the area within half an hour amid shouts of "strike, strike!" - referring to a call for a general strike on Monday.

Hundreds of medical professionals also gathered earlier yesterday evening at the nearby Edinburgh Place at the waterfront to show their support for protesters, said one of the organisers Lau Hoi-man.

Meanwhile, local media reported that eight people had been arrested after a raid on an industrial building, prompting about 100 protesters to gather outside nearby police stations. Those arrested include Mr Andy Chan, convenor of the now-banned Hong Kong National Party, RTHK reported.

His arrest would probably not mark a turning point in the movement, said Mr Sean King, a University of Notre Dame Liu Institute for Asia and Asian Studies Affiliated Scholar. "The Hong Kong government's political tone deafness and Beijing's half-threats only remind people why the protesters are out there in the first place," he added.

More protests are expected this weekend, with one planned for today in the popular shopping district of Mongkok, and two more tomorrow.