Former spy Edward Snowden has exposed not only US cyber-espionage but also political fault lines in Hong Kong that are widening as the territory, a proud bastion of free speech and protest, chafes under Chinese rule.

In retreating to Hong Kong and vowing to fight any US extradition attempt, the former CIA analyst is testing the former British colony's civil liberties under its "one country, two systems" framework of semi-autonomy, experts say.

"I'd be concerned if China oversteps its power because every time it does, it opens up more opportunities for it to do so in the future," said Billy Leung, one of several hundred people who attended a rain-drenched rally in defence of the self-styled whistleblower on Saturday.

Hong Kong's government is vowing to let the law take its course in its handling of Snowden, who arrived in the city in late May with a trove of documents on US cyber-spying that he has leaked to the press.

While the US government has yet to file any formal extradition request, a weekend newspaper poll said that half of Hong Kongers opposed sending him back.

Hong Kong, which retained a separate legal system after returning to China in 1997, has an extradition treaty with the United States but Beijing has the potential to veto any ruling, and suspicion is rife that it will step in.

Many analysts say the US-China relationship is too important to be sacrificed over the 29-year-old contractor and anticipate a quiet deal to hand him over, regardless of whether Hong Kong courts rule to let him stay.

"This is going to affect the Sino-US relationship, so Beijing will step in and ultimately, it will have a big say in terms of how this is going to be solved," said Ma Ngok, a political scientist at the Chinese University of Hong Kong.

Suspicion of Chinese meddling is stoked by popular concerns that Beijing opposes universal suffrage in Hong Kong and enforces policies in connivance with the city's pro-business elite via a compliant local government.

"That fear of Beijing interference is always prevalent in Hong Kong on every front," pro-democracy lawmaker Claudia Mo told AFP.

"Most people would tend to suspect that there would be some form of Beijing intervention, not overtly of course," she said.

China last week stonewalled media questioning about the Snowden affair but issued its first substantive comments on Monday, saying that Washington owed the world an explanation about the reach of its cyber-snooping.

The boot is now on the other foot after persistent complaints from the United States -- raised at a recent Sino-US summit in California -- that China systematically steals secrets held online.

Foreign ministry spokeswoman Hua Chunying also dismissed as "completely groundless" claims aired by former US vice president Dick Cheney that Snowden chose Hong Kong because he was an agent of China.

Some Chinese state media say Beijing should in fact be governed by public opinion in the Snowden case. The Global Times said Monday that extraditing him would be a "betrayal" of his trust and a "face-losing outcome" for China.

"The image of Hong Kong would be forever tarnished," it said.

Snowden timed his trip to Hong Kong well. In two weeks, pro-democracy groups will stage their annual July 1 march marking the anniversary of the Chinese takeover. Last year, hundreds of thousands turned out as anti-Beijing sentiment surged.

Beyond the perennial debate about Hong Kong's political system, ordinary citizens have vented anti-China anger on an array of issues ranging from high property prices to rude mainland tourists and shortages of baby milk powder.

"My intention is to ask the courts and the people of Hong Kong to decide my fate. I have been given no reason to doubt your system," Snowden told the South China Morning Post last Wednesday, in his first interview since unmasking himself to the Guardian newspaper on June 10.

In the SCMP interview, Snowden described hacking by the US National Security Agency of mainframe networks in the city and mainland China, raising the hackles both of the Chinese press and of local politicians.

One scenario raised by Hong Kong commentators is that China will want to grill Snowden about what else he knows before it eventually hands him over for prosecution back home.

But Snowden is appealing to popular opinion as much as to the courts -- and that has proved a potent force in Hong Kong in the past, with city authorities backing down on issues when confronted by mass protests.

China calls spy claims against Snowden 'groundless'
Beijing (AFP) June 17, 2013 - China on Monday dismissed as "groundless" claims that a former US intelligence contractor who is hiding in Hong Kong spied for Beijing, as state media said extraditing him back home would amount to a "betrayal".

China relayed its first concrete comment on the Edward Snowden affair, a day after former US vice president Dick Cheney said he was a "traitor" who may well be acting in cahoots with Beijing's communist government.

"I think it is completely groundless," foreign ministry spokeswoman Hua Chunying told reporters when asked if Snowden had spied for China.

Last week, Hua said that she had "no information to offer" on the 29-year-old, a former contractor for the US National Security Agency who has exposed a vast NSA operation tapping phones and computer systems around the world.

Snowden has made a series of press leaks since coming to Hong Kong on May 20, declaring his confidence in the former British colony's judicial independence as he vows to fight against any extradition bid by the US government.

His revelations have ensnared America's leading technology firms, which have conceded to handing over user data to Washington, but only when forced by a court order.

Apple on Monday said it had received between 4,000 and 5,000 data requests in six months from US authorities, days after Facebook and Microsoft released similar information.

US authorities insist their targets are only foreign terror suspects and that their snooping, including an online NSA operation code-named PRISM, has helped to thwart attacks.

But Britain's Guardian newspaper, to which Snowden unmasked himself after coming to Hong Kong, said Monday that his document trove appeared to show also that Britain spied on G20 delegates during meetings in London back in 2009.

Britain used "ground-breaking intelligence capabilities" to monitor communications between officials at two G20 meetings in April and September of 2009, it said, adding that the officials targeted included delegates from NATO ally Turkey and from South Africa.

Snowden has also alleged that the NSA targeted "hundreds" of computer networks in mainland China and in Hong Kong.

Hua said the United States -- which has complained long and hard about alleged cyber-espionage by China -- owed the world an explanation.

"We believe that the US side should pay attention to the concerns and demands of the international community and the public over this issue, and give the international community a necessary explanation," the ministry spokeswoman said.

Her comments came after Cheney said he was "deeply suspicious" about Snowden's decision to go to China, although Hong Kong has its own British-derived legal system and a jealously guarded culture of free speech.

"That's not a place where you ordinarily want to go if you're interested in freedom and liberty and so forth," the former vice president said on "Fox News Sunday".

"So, it raises questions whether or not he had that kind of connection before he did this."

The United States has launched a criminal investigation into Snowden, who has gone to ground in Hong Kong, but has yet to file a formal extradition request to the territory's authorities.

The Global Times, a state-backed Chinese newspaper, said Monday that extraditing Snowden to the United States would be a "betrayal" of his trust and a "face-losing outcome" for Beijing.

"Unlike a common criminal, Snowden did not hurt anybody. His 'crime' was that he blew the whistle on the US government's violation of civil rights," it said.

If he is sent home, the paper said, "the image of Hong Kong would be forever tarnished".

Its commentary came after China's official army newspaper branded the NSA surveillance programme "frightening" and accused the United States of being a "habitual offender" when it comes to covert monitoring of networks.

Half of Hong Kongers believe the city's government should not extradite Snowden, according to a poll published on Sunday, a day after several hundred people braved heavy rain in Hong Kong's first major demonstration in his support.