Whistleblower Edward Snowden was acclaimed Tuesday by WikiLeaks founder Julian Assange as a "hero" defending personal liberty, but US lawmakers clamoured for the NSA contractor's immediate expulsion from his Hong Kong hideout to face justice at home.

Snowden, a 29-year-old technology expert working for a private firm subcontracted to the National Security Agency, has gone to ground after evading a press pack and apparently checking out of his Hong Kong hotel on Monday.

Many in Washington are baying for Snowden's blood after he leaked the NSA's worldwide monitoring of private users' web traffic and phone records, and some social media commentators in China queried his choice of destination.

In coming to Chinese territory, Snowden has "left the tiger's den and entered the wolf's lair", a user calling himself Mr-Edward-Lin said on a Twitter-style "weibo" site.

But Assange urged nations around the world to offer safe haven to the young American, after Snowden told The Guardian newspaper that he had come to Hong Kong on May 20 with a treasure trove of NSA secrets.

"Edward Snowden is a hero who has informed the public about one of the most serious events of the decade, which was the creeping formulation of a mass surveillance state," the Australian told Sky News.

"What other countries need to do is line up to give support to him," said Assange, who has himself been holed up in the Ecuadoran embassy in London for nearly a year after claiming asylum.

Snowden told The Guardian in an interview published Sunday that he chose Hong Kong as a refuge as it has a "strong tradition of free speech", but the semi-autonomous southern Chinese city also has an extradition treaty with the United States.

There has been much speculation about Hong Kong's likely stance in the event Washington asks for Snowden's extradition -- and whether Beijing might intervene, complicating the nations' relationship just after their presidents met in California.

In Hong Kong, pro-democracy lawmaker Albert Ho suggested Snowden may have chosen the financial hub precisely because of Beijing's ability to intervene in any extradition decision.

"America is too powerful a country, so I think he has no confidence in any European countries, or any countries which have good relations with the US," Ho told AFP.

"He may be thinking of China which is big enough to stand against the strength of the US."

Neither Hong Kong police nor the security bureau, which handles immigration and asylum cases, had any comment Tuesday.

The US government appeared to be gearing up for action against Snowden Monday with senior lawmakers branding the leaks as "treason" and saying he should be extradited as quickly as possible.

California Senator Dianne Feinstein -- the Democratic chairwoman of the Senate Permanent Select Committee on Intelligence -- declined to go into specifics but said US authorities were vigorously pursuing Snowden.

"All the departments are proceeding, I think, aggressively," she told US media.

President Barack Obama's spy chief, Director of National Intelligence James Clapper, has described Snowden's leaks as gravely damaging to US security, and referred the matter to the Justice Department, which has launched an investigation.

Snowden told the Guardian he hopes to win asylum in Iceland, but the head of Iceland's Directorate of Immigration said it had received no formal request and said Snowden would have to be on Icelandic soil to make one.

Meanwhile, Russia will consider an asylum request if one is made, a spokesman for President Vladimir Putin said.

The case has turned the spotlight on the United States' widespread use of outside contractors for sensitive intelligence work. Snowden is a former low-level CIA employee who was last employed by private contractor Booz Allen Hamilton.

Snowden said he had gone public because he could not "allow the US government to destroy privacy, Internet freedom and basic liberties for people around the world with this massive surveillance machine they're secretly building".

Snowden flew to Hong Kong after copying at the NSA's office in Hawaii the documents he intended to disclose, the Guardian said.

Under the so-called PRISM program revealed by Snowden, the NSA can issue directives to Internet firms such as Google or Facebook to win access to emails, online chats, pictures, files, videos and more, uploaded by foreign users.

Obama says such surveillance has helped to keep Americans safe from terror. And 56 percent of Americans support the use of phone records in counter-terrorism despite the invasion of privacy, a Washington Post-Pew Research Center poll said Monday.

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