Small groups of anti-government protesters gathered in shopping malls across Hong Kong on Sunday amid sporadic scuffles with riot police, with Chief Executive Carrie Lam away on a visit to Beijing.

In the peak shopping season ahead of Christmas, groups of masked protesters, clad in black, marched through malls chanting slogans including "Fight for freedom" and "Return justice to us".

In the Telford Plaza mall in Kowloon Bay, skirmishes broke out with riot police, who used pepper spray on crowds and wrestled several people to the ground before taking them away.

In Shatin, police fired one tear gas canister outside the New Town Plaza mall, and took away several people, according to media reports, after some entrances and walkways were blocked, glass panels smashed, and graffiti sprayed.

The police said in a statement that some shops had been damaged and that a smoke bomb had been set off. Many shops closed early.

Hong Kong has been embroiled in its worst political crisis in decades since June with anti-government protests posing a populist challenge to China's leader Xi Jinping, complicating ties between China and the United States at a time of heightened tensions including over trade.

Demonstrators have railed against what they see as Chinese meddling in freedoms promised to Hong Kong when the former British colony returned to Chinese rule in 1997.

They also say they are responding to excessive use of force by police. Last Sunday, a protest march drew around 800,000 people, according to organisers, suggesting the movement still has significant public support.

On Hong Kong island, several hundred people, many social workers, gathered peacefully to reiterate demands that include full democracy and an independent inquiry into allegations of police brutality.

Some called for more strikes, while others sat at tables to write Christmas cards to those who have been jailed.

"One of our goals is defending social justice," said Chan, a 20-year-old studying to become a social worker. "We have tried every measure to express our voices ... but the government still doesn't listen. We haven't put enough pressure."

Separately, a pro-government rally drew over a thousand people nearby.

"We don't support any violence in Hong Kong," said Lee Man-kan, a 54-year-old solicitor. Hong Kong leader Carrie Lam is in Beijing where she is due to meet Xi on Monday.

Some observers say the visit could yield fresh directives including a possible cabinet reshuffle of key local officials.

Lam, however, seemed to play that down before she left, saying the first task was to curb violence and restore order.

The government is also planning more public dialogue through social media channels, as well as a second planned town hall session with top officials to try to bridge differences.

Despite the febrile public mood, China maintains it is committed to the "one country, two systems" formula granting Hong Kong autonomy and says it fully supports Lam.