Hong Kong could be in for fresh protests today after the government let lapse a 5pm deadline set by protesters for it to formally withdraw a contentious extradition Bill.

A crowd, many of them students, gathered at the government offices in Tamar before 5pm yesterday to see if the government would accede to their demand after last week's massive rallies in the city.

Student Jacqueline Chan, 16, who turned up at 4.30pm with several classmates, said they were angry with the Hong Kong government.

"Our generation is growing up in a very different environment from that on the mainland. We are not worried about the details of the extradition Bill but the fact that the government wants to have an agreement with the mainland," she said.

"But the government doesn't get what we are concerned about."

In rallying calls circulating on social media, protesters threatened to block the roads leading to the government headquarters in Admiralty and take other action today if Hong Kong Chief Executive Carrie Lam, who has apologised twice in the aftermath of the protests, did not scrap the Bill by the given deadline. The government offices will be closed today as protesters are expected to gather there at 7am.

In addition, the protesters want the government to not label the June 12 protests as a riot, release all those arrested, and take the police to task for abusing their powers.

The extradition Bill, mooted in February, was to allow Hong Kong to send fugitives to jurisdictions it does not have such agreements with, including mainland China.

But Hong Kongers' distrust of the Chinese legal system fuelled fears that they could be targeted under this law with trumped-up charges and would not receive a fair trial or human rights protection.

Mrs Lam had tried to allay such fears by watering down the proposed legislation twice and putting in place additional safeguards.

But many did not buy her explanations that such a law would prevent Hong Kong from becoming a haven for fugitives, and hundreds of thousands took to the streets instead on two consecutive Sundays.

The anger peaked on June 12 when the Bill was to be tabled for a second reading, with protesters surrounding the government complex to cut off access to lawmakers.

Violent clashes erupted, with some protesters throwing bricks and metal poles at police officers, who were outnumbered. To disperse the crowd, officers fired rubber bullets and tear gas.

More than 80 people were injured and 32 arrested, eight of whom were subsequently freed.

The Civil Human Rights Front yesterday made an official complaint against "the excessive use of force" by the police against protesters.

Its spokesman Lee Cheuk-yan, speaking outside Wan Chai police station, said the entire police set-up where the government offices are located in Admiralty is a "life-threatening matrix".

He accused the police of sowing panic among protesters by firing rubber bullets and tear gas.

Mr Lee, a former lawmaker, also called for an independent commission to investigate alleged abuse of authority as "we don't trust the police investigating themselves".

Democratic Party legislator Lam Cheuk-ting also filed a police complaint, accusing Secretary for Security John Lee of misconduct in public office by misleading the legislature.

Police officers were said to have made it difficult for protesters to identify them by concealing their police identification number. However, Mr John Lee told the Legislative Council this week that the design of the police uniforms did not allow enough space to include an officer's identification number.

Said Mr Lam: "Those police officers concealed their police numbers deliberately to conceal their identity and to prevent any investigation into their abuse of power."

Meanwhile, some parents, alarmed that protesters as young as 12 years old took part in the recent rallies, have banded together, calling themselves Umbrella Parents, in a reference to the 2014 "Occupy" movement, where participants armed themselves with umbrellas.

They urged Mrs Lam to respond to protesters' demands, Radio Television Hong Kong reported.

Another rally to oppose the extradition Bill and demand Mrs Lam's resignation has been planned for July 1, the 22nd anniversary of Hong Kong's 1997 handover to China.