Hong Kong (AFP) - Carrie Lam vowed to heal divisions when she became Hong Kong's leader, but her tenure has been marred by massive democracy protests and a crackdown by Beijing that prompted the United States to sanction her.

The 63-year-old devout Catholic took over in March 2017, becoming the first woman elevated to the city's top job.

But she was not popularly elected. Hong Kong's leaders are instead chosen by a 1,200-strong committee stacked with Beijing loyalists, and Lam secured 777 votes.

She vowed to be more responsive to the city's youngsters, who have been at the forefront of a campaign for greater democratic freedoms and measures to combat rising inequality.

"My priority will be to heal the divide," she said, adding that she would resign if she lost popularity. 

Fast forward three years and Hong Kong is more divided than at any time in living memory after months of huge and often violent democracy protests last year.

Now Lam finds herself on a US sanctions list alongside 10 other local and Chinese officials after Beijing imposed a sweeping national security law on the semi-autonomous city. 

The Treasury Department accused her of being "directly responsible for implementing Beijing's policies of suppression".

Huge protests

Born into a low-income family, Lam excelled at her Catholic school and later attended Cambridge University on government funding.

She began her career in the colonial civil service and her rise up the ranks accelerated after Britain handed Hong Kong back to China in 1997, earning herself a reputation for being a fighter and a committed Beijing loyalist.

At one point she and her family had British dual nationality, something Lam gave up as she rose higher in government.

During the 2014 pro-democracy protests she was often the face of the government, debating student leaders and insisting their demands to directly elect the city's leader would not be met.

When she took the top job three years later Hong Kong's democracy movement appeared moribund, ground down by the failure of the 2014 protests to achieve any results and the prosecution of its leaders.

She vowed to be in touch with public sentiment. 

"If mainstream opinion makes me no longer able to continue the job as chief executive, I'll resign," she declared at an election debate.

Then in 2019 she attempted to fast-track a bill that would allow extraditions to China's Communist Party-controlled courts. 

The bid sparked a public backlash and seven straight months of huge and often violent pro-democracy protests that upended Hong Kong's reputation for stability. 

Her approval ratings tanked to historic lows. But staunchly backed by Beijing throughout, Lam hung on, dismissing the protests and portraying them as a foreign plot to destabilise China.

'Snort of contempt'

In June, Beijing imposed its security law aimed at ending the unrest, describing it as a "sword" that would hang over lawbreakers. 

Western nations saw the law as a fatal blow to the freedoms and autonomy that Beijing promised Hong Kong could keep before the 1997 handover. 

Lam backed the law, which was kept secret from Hong Kongers until it was passed, dismissing what she said was misplaced "doom and gloom" surrounding its passage.

A week after the law came into effect, Lam warned people not to "cross the red line".

Lam has previously brushed off the threat of US sanctions, saying she has no assets in the country and does not want to ever travel there. 

"When facing so-called US sanctions against me, I would just laugh it off and give it a snort of contempt," she said last week.

But democracy activists said Lam's international reputation has been heavily damaged.

"I... want to congratulate her elevation to the status of an international pariah," Samuel Chu, a US-based dissident who authorities have issued an arrest warrant for under the new security law, said in a statement.  

"She will be sharing the same label with dictators, mass murderers, terrorists, and Nazis."