Security forces moved in at 3 AM to break up the sit-in by about 2,000 protesters in the semi-autonomous city's central financial district, according to media reports. Hong Kong authorities said 511 demonstrators were arrested for illegal assembly or obstructing public space. Among those arrested were reportedly several pro-democracy lawmakers.

The arrests came after a largely peaceful march on July 1 to mark the day the territory was returned to China in 1997 after more than a century of British rule. The aim of this year's commemoration was to pressure Beijing's Communist Party leaders to introduce democratic reform and allow electoral freedom. Organizers claim about half a million people took place in the protest march.

The rally came just one day after polls closed in an unofficial referendum which saw nearly 800,000 residents - more than a fifth of the city's electorate - cast ballots to urge Beijing to allow opposition democrats to run in a 2017 citywide election for a new chief executive. China's state-run media called the vote an "illegal farce." In a DW interview Mabel Au, director of Amnesty International (AI) Hong Kong, urges Hong Kong authorities to "ensure policing of future protests is in line with international law."

How would you describe the actions taken by Hong Kong authorities after the rally ended?

This was a peaceful and legitimate protest, not an "illegal assembly" as the authorities have attempted to label it. The police action was hasty and unnecessary. The dispersal of peaceful protests should only be taken as a last resort. The protesters said they would leave at 8 AM so it is right to question why the police forcibly removed the demonstrators when they did.

Isn't it the responsibility of Hong Kong authorities to clear the area after the rally has ended?

This was a peaceful and legitimate protest under international law. All those being held solely for exercising their rights to freedom of expression and assembly must be immediately and unconditionally released.

Peaceful assembly is a legitimate and valid use of public space. Under international law, protests do not require approval by the authorities, though advance notice can be requested. Restrictions on the right to peaceful assembly are only permissible under international law if they are necessary to protect legitimate public interest or the rights of others. Restrictions must be necessary and proportionate.

What precedent do you believe the authorities are setting with the mass arrests?

The police response sends a disturbing signal as to how the authorities may deal with any future peaceful protests. Amnesty International urges the authorities to respect the right to freedom of expression and peaceful assembly. The police have an obligation to facilitate the right to peaceful assembly.

Why would Hong Kong police ask the media to leave the demonstration site before the protesters were removed?

The request for journalists to leave the protests was wrong and is deeply worrying. Many will see the call as part of the Hong Kong authorities' growing hostility to press freedom.

Pro-democracy group Occupy Central has said it will stage a mass sit-in in Central later this year unless authorities come up with acceptable electoral reforms. What impact could the mass arrests have on future protests, especially for the Occupy Central movement?

The police action today was premature and unnecessary. In the past, the Hong Kong authorities have had a good record in respecting the right to freedom of expression and peaceful assembly. However, there have been worrying signs in recent years, this morning's response by police being the latest. Amnesty International urges the authorities to ensure policing of future protests is in line with international law.

What role do you think the Beijing government played in the decision to stop the sit-in?

There is increasing concern in Hong Kong with the growing influence of Beijing in the city's affairs. However, it would be speculation to say what Beijing's role in the response to the protest was either directly or indirectly.

Mabel Au is director of Amnesty International Hong Kong,