Protesters surrounded the Wan Chai police base in the city's centre to present complaints to local authorities about the now-suspended contentious extradition bill and to denounce the oppressive and poor management of the crisis, reports Efe news.
Activists remained on the streets until the early hours of Thursday morning and left after a confrontation with riot police.
The crowd also demanded the release of all detainees in clashes with police earlier this month and urged Police Commissioner Stephen Lo to meet with them face-to-face.
There was some tension during the protest when people set up barricades on roads, painted the outside of the building with slogans critical of the police and locked officers inside.
Public broadcasting service Radio Television Hong Kong reported a police spokesperson saying "it is unacceptable for protesters to block the roads and surround Police Headquarters (...) hundreds of people who besieged Arsenal House on Wednesday night were seriously affecting police work and inconveniencing the public".
Although he said that the police "respects the public's right to peaceful assembly", he urged protesters "to disperse as soon as possible, and be considerate in expressing their views".
Hours earlier, protesters had stated through a manifesto that democracy and freedom were universal, inviolable values and criticized China for breaking its promises and failing to respect the 'one country, two systems' principle.
They also called on G20 leaders to address the extradition bill as part of the agenda for the summit on Friday and Saturday in Japan, and to defend rights and freedoms in Hong Kong.
The activists' goal was to take advantage of the summit to give a greater platform to their cause and comes after China's Assistant Foreign Minister Zhang Jun said on Monday that China will not allow Hong Kong protests issue to be addressed at the summit.
Hong Kong activists also raised more than HK$6.7 million ($858,000) Wednesday in a crowd-funding campaign to call for international pressure during the G20 summit to be attended by Chinese President Xi Jinping and Hong Kong Financial Secretary Paul Chan.
Millions of people have protested in recent weeks in Hong Kong against the extradition bill pushed by the local government that could allow alleged criminals to be sent to several jurisdictions, including China.
Opponents of the bill, which Hong Kong Chief Executive Carrie Lam has put on hold because of the protests, fear that the law may facilitate the transfer to mainland China of activists, journalists and human rights workers to be tried by Chinese justice, which does not offer sufficient protections.
In addition to Thursday's demonstration, activist organisations will participate in another on July 1 on the anniversary of the transfer of British sovereignty of Hong Kong to China in 1997.
( With inputs from IANS )