Hong Kong's tough pro-Beijing number two Carrie Lam announced her bid to lead the deeply divided city Thursday after stepping down from her current post.

Lam is deputy to Hong Kong's unpopular leader Leung Chun-ying and rose through the ranks as a career civil servant before taking public office.

The city has become sharply polarised under Leung, whose term has been marked by anti-Beijing protests. Opponents cast him as a puppet of the Chinese government squeezing the semi-autonomous city's freedoms.

While Lam is less hated than Leung, critics fear she will take a similar hard line if she wins the leadership at elections in March.

Lam, who has worked in government since 1980, would become the city's first woman chief executive.

She said Thursday she was stepping down as deputy leader in order to stand for the top job.

If her resignation is accepted by Beijing, she will run for chief executive she said.

"There is only one reason for me to resign at this juncture," Lam told reporters.

"I intend to prepare to contest in the upcoming chief executive election."

She said it had been an "honour and a privilege" to have served the people of Hong Kong for more than 36 years.

Lam ended the brief press conference without taking questions, with one reporter shouting after her "Are you going down the path of CY?" referring to current leader Leung.

Political analysts said Lam was considered by the public to be a capable leader.

"The worry is that her ambition might prompt her to side exclusively with Beijing because that's where her power comes from," Willy Lam, a professor at the Chinese University of Hong Kong, told AFP.

The city leader is chosen by a 1,200-strong committee of representatives of special interest groups, weighted towards Beijing.

Mass pro-democracy rallies in 2014 called for fully free leadership elections but failed to win concessions.

Critics are already accusing Lam of trying to gain favour with Chinese authorities by pushing through a museum project which would bring historic cultural artifacts to Hong Kong from Beijing's Palace Museum.

They say the project is cultural brainwashing and accuse Lam of failing to consult the public on the plans.

Lam was also vilified by pro-democracy activists during the 2014 rallies for being a Beijing stooge.

The city's finance secretary John Tsang resigned in December and is expected to enter the race soon.

Nicknamed "Mr Pringles" by local media for his resemblance to the crisp brand's mascot, Tsang is seen as a more moderate alternative to Leung and Lam.

While Tsang and Lam are considered the strongest contenders, others have already thrown their hats in the ring.

Former Hong Kong security chief Regina Ip, who is loathed by the city's pro-democracy camp, declared her candidacy last month.

Retired judge Woo Kwok-hing, who has said he will prioritise political reform, has also declared he is running.