Hong Kong's democracy demonstrators are winning unexpected support from pockets of the city's much-vilified mainland Chinese community, who are defying Beijing's hard line on the protests and a social media backlash from their peers.

Hong Kongers have long had a testy relationship with mainlanders, who are often derided for swamping the already densely crowded financial hub and usurping resources, from hospital beds to baby formula.

The city's protests over Beijing's refusal to grant fully free elections have drawn insouciant shrugs and nationalistic rants across much of the mainland, with small knots of sympathisers swiftly detained by authorities.

But some mainlanders in Hong Kong are bravely showing up at the rallies that erupted two weeks ago, lending logistical and ideological support and revelling in what is strictly forbidden on the Communist mainland -- rooting for democracy.

"On the mainland, you can be thrown in jail for your beliefs," said Li, a 21-year-old sociology student from southern Guangdong province.

"Coming out at protests in Hong Kong, shouting slogans for democracy, standing up for what you truly believe in is a liberating experience."

Li, who requested that her real name be withheld, never converses in Mandarin at protests -- only Cantonese with a "Taiwan accent" -- and sticks with Western peers from her university in Hong Kong, masking her face to "prevent any trouble" for her parents back in Guangdong.

The number of such supporters is hard to ascertain but the trend reinforces the nightmare scenario for Beijing of a possible domino effect that would see the mass revolt in Hong Kong spread to the mainland.

Beijing has said that candidates for Hong Kong's leadership election in 2017 will be vetted -- infuriating protesters who call it "fake democracy".

Tensions flared at the city's main rally site Monday as masked men descended on barricades, triggering clashes with protesters, hours after police had removed some barriers in a dawn operation.

- Facebook backlash -

But the odds of the protest movement extending to the mainland are slim, says Hong Kong University student Xin, judging by the reactions from her fellow mainlanders on Facebook -- some openly supported the use of tear gas on umbrella-wielding Hong Kong protesters on September 28 in a police move that grabbed the world's attention.

Facebook is officially banned in mainland China but it is possible to use virtual private networks (VPNs) to bypass the country's vast censorship apparatus.

Xin, 24, says her Facebook timeline turned into a battlefield when she began posting pictures of the protests from the roof of her 22-storey building in Causeway Bay district, where she set up a free WiFi hotspot to enable demonstrators to post live updates on social media.

"Hong Kongers are spoilt and ungrateful."

"The city won't survive a day without China."

"What democracy? We've already given you too much freedom."

Infuriated by Xin's support for Hong Kong's Umbrella Revolution, some of her "nationalist minded" mainland friends abandoned her Facebook page.

The protests are reported to have triggered a "collective war of unfriending" on social media between mainlanders on the two ends of the political divide, the Hong Kong-based newspaper Ming Pao Daily said in a recent article.

Many of those trading barbs from the mainland have limited access to the realities in Hong Kong because of the "sanitised" coverage in the heavily censored national media, Xin said.

"I call up my mother and she curiously asks me, 'Oh but why are Hong Kong people behaving so badly?' She doesn't have the slightest clue."

One Chinese television report said that Hong Kongers were enjoying "fresh air" at the city's protest-hit Tamar Park, at the peak of the demonstrations, Xin added.

- Stereotyping mainlanders -

But despite their zealous support for democracy, it hasn't been easy for mainlanders to win over Hong Kong protesters.

In a video that went viral on YouTube, a mainland supporter is seen booed and heckled in the city's Mongkok district by an emotionally charged crowd of protesters who mistake her for a pro-government member. https://www.youtube.com/watch?v=RubSzEsyFi0

"I was there in 1989," the middle-aged woman says in Cantonese with a heavy mainland accent, apparently referring to 1989 Tiananmen Square crackdown in Beijing.

"I support students, I support universal suffrage," she pleads with the protesters in a high-pitched voice.

But the crowd erupts into rhythmic clapping and a raucous chorus of "Happy Birthday", which has become a popular anthem among protesters to signal pro-Beijing rivals.

"I was in the front row when you were tear-gassed on September 28. I was telling the students to protect themselves from the fumes like this," the woman says, pulling out a transparent mask and wrapping it over her face, but only a few stop and pay attention.

The video broke Jie's heart.

The 25-year-old mainlander from southwestern Sichuan province said she stands for democracy but is put off by the "chauvinistic attitudes" in Hong Kong towards mainlanders.

A mainlander is typically stereotyped as a country bumpkin with a lot of money, she says.

In the year that she has been a student in Hong Kong, she has often heard the phrase "keung gwok yun" -- derogatory Cantonese slang meaning "strong country people", an apparent dig at China's regional hegemony.

A Hong Kong University poll in June showed a spike in the number of people identifying themselves exclusively as Hong Kongers, while those identifying themselves as Chinese fell to the lowest levels since 1997.

"Hong Kongers and mainlanders are growing further and further apart everyday," said Jie, who did not want to be identified by her real name.

"Why aren't we listening to each other any more?"