“If I was him, I’d be getting out of here and heading to a sympathetic jurisdiction as fast as possible and certainly before the United States issues a request for his extradition,” said lawyer Kevin Egan, who has dealt with extradition cases in the city.

“The attitude of the judiciary here seems to be if Uncle Sam wants you, Uncle Sam will get you.”

The big unknown in this case is China. Although it has a degree of autonomy, Hong Kong ultimately answers to Beijing and China could exercise its right to veto any ruling in a local court if the opportunity arose.

So far, there’s been no indication of any moves by Hong Kong law enforcement to approach or question Snowden, last known to have checked out of a luxury hotel in the city’s Kowloon district on Monday.

The Security Bureau declined comment, while the Hong Kong government has said generally it will act in accordance with the law. The Chinese government has not commented on the case.

“In strictly legal terms he’s free to go, but government bodies can always find an excuse to temporise, or stop him,” said Jonathan Acton-Bond, a lawyer who has dealt with high-profile extradition cases in Hong Kong.

The US Justice Department is in the initial stages of a criminal investigation into the revelations, officials in Washington have said.

The key to Snowden’s fate lies in the specific nature of any charges filed against him, if and when they are filed. It will then depend on whether, under Hong Kong law, he’s also charged with a criminal act, without which authorities cannot arrest or take legal action against him.

“If they can’t find the equivalent charge in Hong Kong, they can’t extradite him,” said lawyer and legislator Ronny Tong, who added any protracted extradition battle could become a high-profile test of the city’s rule of law in the face of political pressure from Beijing and Washington.

Sources at Hong Kong law firms have said Snowden has approached human rights lawyers in the city and may be digging in his heels for a legal fight in preparation for the United States laying charges against him.

Snowden, who admitted he disclosed classified information about National Security Agency (NSA) surveillance programs to the Guardian and Washington Post newspapers, is likely to face charges, possibly under the Espionage Act enacted in 1917, experts in the United States have said.

Under Hong Kong laws, an espionage charge could potentially find equivalence under its Official Secrets Ordinance.

The offence of “unlawful use of computers” meanwhile, is included in the list of offences in the extradition treaty between Hong Kong and the United States, and could potentially be used as grounds for extradition, legal experts say.

Either way, should Snowden face a formal extradition bid, he could challenge this in a Hong Kong court, and concurrently make a claim for political asylum in what could be a protracted legal battle that could drag out for months, if not years.

Given the political sensitivity of the case, there’s a chance the United States could pressure China to fast-track any possible expedition request. The scope, however, for Beijing to influence the outcome of court extradition proceedings is limited and has rarely been exercised for cases involving non-Chinese nationals.

Despite China’s ultimate authority over Hong Kong, the financial hub maintains a high degree of autonomy, with its British common law system considered one of the pillars of its success as a commercial and financial hub.

“The extradition system if it’s engaged, follows strict procedures laid down by the law and that’s supervised by the courts,” said prominent Hong Kong lawyer Philip Dykes.

Another lawyer and extradition expert in Hong Kong who declined to be named said even if proceedings were fast tracked by the US and Hong Kong governments and Snowden were arrested, he would have the right to habeas corpus - to be brought before a local court to demand release from unlawful detention.

Geoffrey Robertson, a leading London-based lawyer who has advised WikiLeaks founder Julian Assange in an ongoing extradition case, said Snowden could argue he had not put lives at risk and was a political refugee. But he could consider moving out of Hong Kong.

Speaking after Russia said it would consider granting asylum to the American, Robertson told Reuters: “Mr Snowden would doubtless be safe-but-sorry in North Korea and might find refuge in Russia. A more pleasant environment would be New Zealand where he could join Kim Dotcom in resisting extradition.”

Kim Dotcom is the founder of the Megaupload file sharing site, who is fighting extradition to the United States to face online piracy charges.