Tens of thousands of protesters took to the streets of Hong Kong on Tuesday, calling for the city's embattled leader to quit and demanding greater democracy 15 years after it returned to Chinese rule.

Organisers have said they expected 50,000 people to join the New Year's Day march against Leung Chun-ying, while pro-government groups staged separate and smaller rallies in support of the Beijing-backed chief executive.

Since taking office in July Leung's popularity ratings have tumbled and he has faced a no-confidence vote in the legislature amid a row over illegal structures at his luxury home -- a politically sensitive issue in the city.

"We have to keep voicing our concerns even though the situation is getting worse," 27-year-old university student Billy Li said as the demonstrators marched through the city to the government's harbourfront headquarters.

Holding up posters of Leung portrayed as a vampire and a wolf, the protesters -- some waving flags from the British colonial era -- chanted "Give us universal suffrage immediately" and "Step down, Leung Chun-ying".

Preliminary figures from the police put the crowd at 17,000 and another 1,000 at a separate anti-Leung protest organised by a radical political party People Power. Police said they arrested a 62-year-old man for displaying a defaced Chinese flag.

Leung has acknowledged and apologised for the structures, which were built without planning permission and include a wooden trellis and a glass enclosure.

He became chief executive after his rival for the post, Henry Tang, was brought down by a row over illegal structures at his own home.

Demonstrators have used the scandal to press for universal suffrage in choosing the leader of Hong Kong. It was returned to Beijing in 1997 but maintains a semi-autonomous status, with guarantees of civil liberties such as the right to protest not seen on the mainland.

Leung was elected in March by a 1,200-strong election committee dominated by pro-Beijing elites, amid rising anger among the city's seven million inhabitants over what many perceive to be China meddling in local affairs.

Beijing has said the city's chief executive could be directly elected in 2017 at the earliest, with the legislature following by 2020.

"Because we don't have a democratic government, most of the policies introduced by this government do not directly reflect the interests of the people," Jackie Hung, a spokeswoman for protest organiser Civil Human Rights Front said.

Thousands of Leung's supporters chanted "Support CY (Leung), support the government" at a separate rally earlier. Organisers claimed a turnout of 60,000 while police put the figure at around 8,000.

In a bid to tackle discontent, Leung has banned mainland Chinese women from giving birth in Hong Kong to secure residence rights for their children.

He has also introduced policies to prioritise housing for locals, a move which analysts say was a reaction to mainland buyers who were blamed for pushing up prices in one of the world's most expensive property markets.

But a survey released by the University of Hong Kong's Public Opinion Programme on Monday showed those dissatisfied with the city's development rose 11 percentage points to 46 percent compared to a year ago.

"People are getting more dissatisfied because they don't trust Leung, judging from how he handled the illegal structures issue," political analyst Joseph Cheng from Hong Kong's City University told AFP.

"They marched to tell Beijing and the world that they want universal suffrage."

A government spokesman said in a statement that the authorities would listen to views expressed at the mass demonstration "in a humble manner".

About 1,000 police were reportedly deployed for Tuesday's marches, following scuffles over the weekend at a pro-government rally that saw two journalists assaulted.