A former top government adviser condemned Hong Kong's leader on Tuesday, calling for her to "resign in shame" over a deadly Covid-19 wave that has clogged the city's healthcare system and sent elderly deaths soaring.

Former government adviser Wong Chack-kie joins a chorus of pro-Beijing loyalists in criticising Chief Executive Carrie Lam at a politically sensitive juncture for the city with a new leader to be selected by July 1.

Key Chinese officials -- including President Xi Jinping -- are also expected to be in town by that date for the 25th anniversary of Hong Kong's handover from Britain to China.

But Hong Kong's 740,000 plus cases and 4,300 deaths in under three months -- mostly inside the city's care homes -- have seen Lam's administration rebuked for its low vaccination rates and unclear messaging around potential lockdown and testing measures.

"If a leader is of any virtue, he or she should resign in shame after seeing so many elderly people die of policy faults," Wong wrote in an opinion piece published Tuesday in the Ming Pao newspaper, calling the crisis a "man-made calamity".

"After the situation got out of hand, all the officials knew was to shirk the responsibilities by repeatedly emphasising that the outbreak had overwhelmed the government's capacity," the former top adviser to Lam's predecessor Leung Chun-ying said.

The outbreak hit as Beijing remoulds Hong Kong in its own authoritarian image after huge and sometimes violent democracy protests erupted in 2019.

Hong Kong's over 740,000 cases in under three months has seen Lam's administration skewered for its low vaccination rates and unclear messaging
Hong Kong's over 740,000 cases in under three months has seen Lam's administration skewered for its low vaccination rates and unclear messaging AFP / DALE DE LA REY

It imposed a sweeping national security law that criminalises dissent, and a new "patriots only" legislature that vets anyone standing for public office for their political loyalty.

Hong Kong's fifth wave has been the first real test for the "patriots only" government.

Researchers estimate the infection toll is significantly higher than official figures indicate, likely reaching half the city's 7.4 million population.

The head of the Beijing-based Chinese Association of Hong Kong and Macau Studies think tank warned Sunday that "accumulated discontent... may lead to political instability".

"That will undermine the authority of 'patriots ruling Hong Kong,'" Lau Siu-kai said on television.

Senior counsel Cheng Huan and business mogul Allan Zeman, both openly pro-establishment, have also called on the government to provide a roadmap out of the crisis.

Wong's missive comes days after his former boss Leung was seen smiling and conferring with Xi, after the closing session of the National People's Congress in Beijing Friday.

Lam has repeatedly declined to disclose whether she will seek a second term.