Hong Kong may not prove to be a haven for US whistleblower Edward Snowden, but any extradition bid will be long and complicated, according to experts in a city that cherishes civic freedoms despite Chinese sovereignty.

Snowden, a 29-year-old government contractor, is believed to be in the southern Chinese city after leaking details of a secret US Internet surveillance programme.

The former CIA technical assistant disclosed his role in a video interview from Hong Kong posted on the website of The Guardian newspaper Sunday, saying he chose the city as a refuge because of its "strong tradition of free speech".

Hong Kong and the US signed an extradition treaty a year before the territory was handed over from Britain to China in 1997.

But the treaty, signed with Beijing's "authorisation", gives the right to refusal should extradition impinge on the "defence, foreign affairs or essential public interest or policy" of China.

This effectively means Beijing, which maintains control over Hong Kong's foreign relations and defence policy, has a veto.

Snowden's revelations come just after US President Barack Obama and China's leader Xi Jinping held their first summit where they talked bluntly on issues such as cybersecurity but also forged a personal rapport.

Political analyst Johnny Lau said that the two countries, who have a range of difficult economic and security affairs to navigate, have little motivation to stir trouble over the Snowden case.

"We have to look at the what are the interests involved. This is only a minor episode and it is not going to affect the big setting where China and the United States cooperate," the veteran China-watcher told AFP.

Kerry Brown, professor of Chinese politics at the University of Sydney, said whereas it would normally be the US hosting Chinese dissidents, it was "amazing" to see the roles of the two countries reversed.

"It might not hand the guy back, but will now have to seek the same diplomatic solutions that the US did over (Chinese dissident) Chen Guangcheng. Nice to see the boot on the other foot for once," he said in an email to AFP.

Hong Kong is a semi-autonomous territory with its own political and legal system that guarantees civil liberties not seen on the mainland.

The freewheeling city's strong culture of free protest was demonstrated last week, when tens of thousands marked the 24th anniversary of China's bloody Tiananmen Square crackdown.

The city is home to a lively and outspoken civil society network, and rights issues resonate with a population which chafes at Beijing's heavy hand.

Hong Kong's Foreign Correspondents' Club said the case was a strong test of the government's commitment to freedom of expression and would watch closely "how it responds to any pressure from authorities both in Washington and Beijing".

Journalists were on the hunt for the whistleblower, with a receptionist at the city's Mira Hotel saying an Edward Snowden checked out Monday afternoon, but declining to provide a description or to say when he checked in.

The Hong Kong government said it did not comment on individual cases. "All cases will be handled in accordance with the laws of Hong Kong," it said in a statement. The US consulate also declined to comment.

Any application would have to proceed through Hong Kong's courts before Beijing could intervene, but there is precedent for it to do so, including a legal saga over the rights to residency of children of Hong Kong permanent residents from mainland China.

The court case could take months and Civic Party legislator Ronny Tong, who is also a barrister, said Washington would have to pinpoint the offences Snowden had allegedly committed to satisfy the extradition treaty.

"The act itself would need to be shown to be a criminalised act in both jurisdictions," he said.

"We have no official secrecy law. The current laws only bind government servants and officials and does not apply to individuals.

"If it is not a criminal act in Hong Kong the United States will have difficulties in seeking an extradition."

Authorities in the city however have some history of cooperation when it comes to working with overseas governments.

Hong Kong authorities raided offices, domestic premises and luxury hotel suites of Megaupload founder Kim Dotcom as a part of a worldwide FBI Internet privacy investigation in 2012.

And at the end of last year Libyan Sami al-Saadi threatened to sue the Hong Kong government for damages after he was arrested in the city in 2004 and illegally transferred to Libya, where he was tortured.

Veteran pro-Beijing lawmaker Regina Ip, a former Hong Kong secretary for security, said Monday that the city's administration was "obliged to comply with the terms of agreements" with the US and that Snowden should leave.

But Audrey Eu, chairwoman of the Civic Party which is one of the city's key pro-democracy political parties, praised Snowden's "brave actions in the public interest" and said the independent judiciary would serve him well.

"I am pleased to hear Mr. Snowden says he chose Hong Kong because this is a city that treasures freedom," she told AFP.

"I believe he will also find that we have an independent judiciary if it ever comes to extradition or rendition proceedings.

"Under the treaty, Hong Kong courts will not surrender the fugitive if this is political prosecution."