A group of protesters have attempted to force their way into the Legislative Council building, the center of Hong Kong's government, as the semi-autonomous city prepares to mark the anniversary of its return to Chinese rule.

Hundreds of mainly young, masked protesters tried to break into one of the side doors of the government headquarters using metal bars and trolleys as battering rams early afternoon, Monday.

Riot police, wearing helmets and armed with shields, were visible inside the building but appeared reluctant to confront the crowds.

Pro-democracy Hong Kong lawmakers were earlier seen attempting to talk down protesters, but to little avail.

The escalation in tensions follows a morning of clashes between hundreds of protesters and riot police, amid an ongoing political crisis over a controversial extradition bill.

Demonstrators took to the streets early Monday, blocking several key roads leading to the main government building.

Protesters had hoped to block or interrupt an official flag raising ceremony marking the occasion, attended by the city's embattled Chief Executive Carrie Lam.

The ceremony marked a rare public appearance for Lam, who was forced to publicly apologize for the introduction of the extradition bill last month.

That bill has been shelved and Lam says there are no plans to restart the legislative process, but protests have not stopped, with a march on June 16 attracting around 2 million people, according to organizers.

Protesters fear the bill could be used to extradite residents to mainland China for political or inadvertent business offenses and are pushing for it to be shelved completely.

Since May's mass march, smaller demonstrations have targeted police and government offices, shutting them down and trapping police officers in their headquarters for hours.

Many protesters are angry over police use of tear gas and rubber bullets to force people off the streets on June 12, when protesters successfully blocked off the city's legislature and prevented lawmakers from debating the extradition bill.

In her speech at the flag raising ceremony Monday, Lam promised to “ease anxiety in the community, and to pave the way forward for Hong Kong.”

Hundreds of thousands are expected to take the streets later Monday, in what organizers hope will be the largest protest against the extradition bill since June's record-breaking turnout.

Beijing stands behind leader

While Beijing has stood by Lam, she is facing criticism from all sides for her handling of the crisis.

Lam says the bill was her idea, not Beijing's, and she's taken responsibility for a rushed roll-out and failure to communicate with the public, who fear it could be used to extradite anyone in the city across the border to China to face political charges.

Even much of the city's business community, traditionally conservative and unwilling to get too involved in politics, came out against the bill, and some pro-government figures criticized Lam for pushing it through the legislature against proper procedure.

She justified that move as necessary in order to extradite a wanted murderer to Taiwan, but that justification was made useless by Taipei's statement in May that it would not accept any transfer under the controversial bill.

Protests and anger over the bill have reinvigorated an opposition movement that had appeared to be in the doldrums after repeated losses in the wake of the 2014 Umbrella Movement.

Now Lam is facing not only continued demonstrations against the bill — and demands for her resignation — but also a return to the issue behind the 2014 protests, that Hong Kongers are not able to choose their own leader.

A key reason Beijing was keen to keep Lam in place, even if she wanted to resign, is that losing her would require choosing another chief executive within six months. Currently that is done by an election committee heavily stacked in Beijing's favor, and renewing this process would be sure to restart an angry political debate that had been safely kicked down the road to 2022.

Now that issue seems to be coming to the fore anyway, piling more pressure on Lam and starting new headaches for her bosses in Beijing.