HONG KONG — Huge crowds of protesters thronged the streets of Hong Kong on Sunday afternoon, hours after President Hu Jintao of China swore in a new chief executive and cabinet for the territory.

Surging down broad avenues between high-rises in a central shopping district, the protesters marched toward two government office complexes carrying a variety of banners. A wide range of causes were represented, including greater democracy in Hong Kong and calls for better state pensions and day care.
But the most common theme was derision toward Hong Kong’s new chief executive, Leung Chun-ying. He was widely portrayed as a wolf because democracy activists contend that he is “a wolf in sheep’s clothing,” whose sympathies for the Chinese Communist Party may lead him to roll back some of the city’s cherished civil liberties — although Mr. Leung has denied this.
“We worry that as he becomes our leader, he will betray our freedoms and civil rights,” said Juno Wu, a 24-year-old librarian.
As people continued to stream out of Victoria Park, where the protest began, organizers and the police had no immediate estimate of the number of marchers. The protest took place after Mr. Hu had already flown out of Hong Kong at midday, after the inauguration of Mr. Leung.
An unexpected element of the demonstration that may discomfit Beijing officials lay in the participation in the march of hundreds of mainland Chinese who carried banners denouncing the confiscation of their farms for government-backed real estate projects in communities near Hong Kong.
“It is not possible to protest in China, so we come here instead,” said a middle-aged mainlander who insisted on anonymity to avoid government retaliation.
Mainland Chinese have frequently attended candlelight vigils and other protests here, sometimes as participants and sometimes as curious onlookers, but usually at night. It is unusual for them to carry large banners through the streets in broad daylight.
Britain returned Hong Kong to Chinese rule in 1997 after British and Chinese leaders promised considerable autonomy to the city until at least 2047.
Earlier Sunday, the swearing-in of Mr. Leung was briefly disrupted when one of the 2,300 guests began shouting as Mr. Hu addressed the audience. An unidentified man asked Mr. Hu to end one-party rule in mainland China and to remember June 4, a reference to the date of the military crackdown in 1989 on protesters at Tiananmen Square in Beijing.
Security guards quickly escorted the man out of the convention center room where the ceremony was being held.
Mr. Hu promised the audience at the ceremony that Beijing would uphold the “one country, two systems” model in place since the handover. Beijing has promised that Hong Kong’s civil rights — including free speech, independent courts and a free media — will be preserved, along with its capitalist economic system.
Opinion polls by academic institutions suggest that public sentiment here toward China is at its lowest point since the handover in 1997. That partly reflects controversy this year over human rights abuses on the mainland, most notably the suspicious death of a Tiananmen Square dissident a month after he was finally released from prison.
Wealthy mainland families seeking to diversify their investments and protect them from taxes or politically motivated confiscation have poured huge sums into the Hong Kong real estate market, driving prices to record highs this month that few Hong Kong citizens can afford. Affluent mainlanders seeking to avoid the “one child” policy and to obtain Hong Kong passports for their offspring have flooded maternity wards at the city’s hospitals in recent years; Mr. Leung has already promised to halt the influx of pregnant mainlanders starting next January by reducing to zero the annual quota for mainland mothers giving birth in Hong Kong hospitals.
As he took office, Mr. Leung spurned speaking in Cantonese, the Chinese dialect here, and used Mandarin, the dominant dialect on the mainland, to say his government would begin immediately to confront the array of social issues confronting the territory. In June, the government here said the divide between rich and poor, already the greatest of any economy in Asia, had reached its highest mark since records began being kept in 1971.
Iris Wong, a 26-year-old Hong Kong resident, said many of the issues confronting the city are linked to one another.
“There isn’t one issue I’m concerned about more than others,” she said. “They’re all connected. If we had democracy and a political system that was not dominated by a few wealthy people, we could begin to address economic problems.”
Before the morning inaugural ceremony, a small group of demonstrators burned effigies of Mr. Leung, calling on him to step down. Hong Kong residents are unable to directly vote for top government positions. Rather, a 1,200-person election committee made up of various special interests selects the chief executive.
When Mr. Leung entered the election campaign last autumn, he was widely seen as an underdog partly because many Hong Kong residents saw him as a close ally of the Chinese Communist Party. His rival, Henry Tang, the scion of a wealthy manufacturing family originally from Shanghai, had strong support from the influential Shanghai faction in mainland Chinese politics.
But Mr. Tang’s candidacy imploded in a series of setbacks, notably the disclosure early this year that an extensive basement had been built under his wife’s house without planning permission from the government or the payment of real estate taxes and fees. So it came as a surprise a week ago when it turned out that Mr. Leung had six illegal structures at his 500 million Hong Kong dollar, or about $64 million, home in one of Hong Kong’s most prestigious neighborhoods.
Mr. Leung, one of the city’s most successful real estate surveyors, has publicly apologized and said that four of the structures were already there when he bought the house in 2000, including a basement for which taxes and fees had not been paid, and that he did not realize the other two, a glass canopy and a trellis, were illegal.
The disclosure of Mr. Leung’s real estate transgressions has particularly hurt his image because a central theme of his campaign was to address the city’s acute shortage of affordable housing. Among the housing issues facing him as he takes office is whether to force the demolition of thousands of illegal structures in outlying areas; whether to halt the encroachment of residential construction on parks and other government land; and whether to step up the pace at which the government makes land available for public and private housing projects.
Hilda Wang and Jacob Fromer contributed reporting.