And there is talk in political circles that former chief executive Carrie Lam Cheng Yuet-ngor is among potential candidates for successor.

With the election for Hong Kong deputies looming, sources said a third of the 36 incumbents, who have reached 70 years, will likely step down.

Although there is no official age limit, it is common for those aged 70 and above to retire.

Other deputies - including heavyweight Cheng Yiu-tong, Ip Kwok-him from the Democratic Alliance for the Betterment and Progress of Hong Kong and lawmaker Michael Tien Puk-sun - are also expected to skip reelection.

Sources said Tam told colleagues earlier that he will not seek reelection. But he told the media he will announce his decision on Monday.

Only two other people have taken up the key post before - businessman Tsang Hin-chi and former Legislative Council president Rita Fan Hsu Lai-tai.

It is understood Tam's successor must be a politician trusted by Beijing and who is familiar with Hong Kong and mainland affairs.

At least two politicians said that they have heard that Lam, 65, is being tipped as a candidate.

A source close to Lam said a potential hurdle is that an NPC Standing Committee delegate's rank is lower than state leader.

Former chief executives Tung Chee-hwa and Leung Chun-ying have state leader status as vice chairmen of the Chinese People's Political Consultative Conference National Committee.

CPPCC National Committee members Starry Lee Wai-king and Rock Chen Chung-nin are expected to join the race as deputies.