Hong Kong's tough former deputy leader Carrie Lam, widely seen as China's favourite in an upcoming election for the top post, pledged Monday to end the divided city's "heartache" as she announced her candidacy.

Lam was deputy to the unpopular current chief executive Leung Chun-ying until she resigned to contest the poll, but is a less disliked figure.

Leung is vilified by the city's pro-democracy camp as a puppet of Beijing squeezing the semi-autonomous city's freedoms.

Hong Kong has become sharply polarised during his four-year term, which has been marked by anti-Beijing protests.

Speaking for the first time to confirm her candidacy for the leadership vote in March, Lam was repeatedly asked if she would be another version of Leung, as some critics fear.

She said she would try to build consensus and "restore faith and hope".

"In recent years, some situations have emerged in Hong Kong that have made people very concerned and worried, sometimes even caused heartache," Lam, 59, told reporters.

"Like many of you I am worried about the discontent," she added, saying her supporters believed she had the ability to "resolve Hong Kong's deep contradictions".

But Lam, who spent 36 years in government, stopped short of acknowledging the discord between pro-Beijing and pro-democracy supporters, saying the public was more concerned about income inequality and sky-high housing costs.

"While democracy is something we should go for, we have to take a very pragmatic stance on whether we have the right environment for us to revive the discussion on another political reform in Hong Kong," she said.

Also poised to announce his candidacy is former finance secretary John Tsang. Opinion polls show him and Lam well ahead in opinion polls, with two other candidates trailing far behind.

But the public will not vote for the next leader following the rejection of political reforms put forward by Beijing.

The next leader will instead be chosen by a committee of 1,200 mainly pro-Beijing representatives.

Lam had presented the reform package, seen by critics as fake democracy, which triggered mass street protests in Hong Kong in late 2014.

The plan offered the public its first chance to vote for the city's leader but said all candidates must be approved by a loyalist committee.

The package was eventually voted down by pro-democracy lawmakers.

Political analyst Willy Lam said Lam was unlikely to touch on political reform until later in her tenure if she wins.

He said she needed to "build bridges" with the pro-democracy camp and show she was not afraid of confronting Beijing.