Hong Kong marks the 15th anniversary of its handover to China on Sunday, but protests targeting visiting Chinese President Hu Jintao will highlight growing misgivings over life under mainland rule.

The former British colony has reaped great economic rewards since the July 1, 1997 handover, as its finance sector plays banker to China's boom and its property tycoons cash in on the new wealth of mainland investors.

But instead of celebrating the relationship, Hong Kongers are expected to take to the streets in their thousands on Sunday to demand greater democracy and rail against Beijing's meddling in local affairs.

"Civil society is strong and vibrant and vocal, and I guess that is also the product of the attempts to suppress people's rights," Democratic Party vice chairwoman Emily Lau told AFP.

"Because they see the signs, so the people rise up."

Hu is due to arrive in Hong Kong on Friday to attend official anniversary events as the communist authorities in Beijing stress unity and stability ahead of their own once-in-a-decade leadership change later in the year.

Police have beefed up security ahead of Hu's visit, after Chinese Vice Premier Li Keqiang was dogged by a spate of protests during his visit last year while journalists and protesters complained of heavy-handed police treatment.

Under the "One Country Two Systems" governing arrangement, Hong Kong is a semi-autonomous region within China, with its own currency and mini-constitution guaranteeing freedoms and liberties not seen on the mainland.

People are free to protest and speak their minds, there are no restrictions on the Internet and many lawmakers are directly elected even if the top leader, known as the chief executive, is picked by a pro-Beijing electoral committee.

Hong Kong's cherished freedoms were on display earlier this month when up to 180,000 people attended a candlelight vigil to commemorate the 1989 Tiananmen Square crackdown -- a taboo subject on the mainland.

Two weeks ago thousands more marched through the city centre demanding an investigation into the suspicious death of dissident Li Wangyang, a Tiananmen democracy activist who was found hanged in his mainland hospital ward.

On top of grievances over human rights and democracy, there have also been protests over the widening gap between rich and poor arising from China's economic influence.

Property prices have surged 95 percent over the past five years and swathes of Hong Kong have turned into luxury shopping playgrounds for cashed-up mainlanders.

"The heavy economic dependence on the mainland has exacerbated Hong Kong's inner contradiction," Chinese University of Hong Kong history professor Willy Lam said.

"The ruling sectors -- the government, big business -- feel they must not ruffle feathers in Beijing so as to preserve the economic advantages. But the intellectuals and the young people do not feel this way."

Hong Kong's median home price is 12.6 times the annual median household income, according to research group Demographia. That compares to a multiple of 3.1 in the United States and 5.0 in Britain.

Many Hong Kongers, even those in the upper-middle income bracket, can no longer afford to buy their own apartments. Those on low incomes are being pushed into tiny rooms known as "cubicles".

The property squeeze has fuelled anger at Hong Kong's leader-elect Leung Chun-ying -- whose inauguration Hu will also attend Sunday -- who was forced to apologise over revelations of illegal improvements to his home.

Leung's main rival in the election race, Henry Tang, was engulfed in scandal during the campaign when he admitted to having built an elaborate entertainment den below his luxury home without construction permits.

Leung was chosen to replace outgoing chief Donald Tsang by a pro-Beijing committee in March, promising to improve governance and uphold the rule of law.

But the selection of the 57-year-old millionaire property consultant has already attracted protests drawing thousands of people decrying Beijing interference in the political process.

The mainland's economic heft can be felt in everything from demand for school places, maternity beds and baby formula to the choking smog that often hangs over Hong Kong's spectacular Victoria Harbour.

Tensions flared in January when a Beijing professor, angered at an online video showing Hong Kongers berating a mainland girl for eating on a train, called the city's residents "running dogs of the British colonialists".

A Hong Kong group responded by taking out a full-page ad in a local newspaper branding mainlanders as "locusts".

A poll released last week by the University of Hong Kong showed mistrust among Hong Kongers toward Beijing at a new post-handover high of 37 percent.

"Hong Kong is going to be a part of China -- it's a part of China but that integration is going to take 50 years," said former Hong Kong lawmaker Christine Loh, head of the Civic Exchange think tank.

"So where are we? It remains an evolving picture."