Former US spy Edward Snowden Wednesday vowed to fight any bid to extradite him from Hong Kong and promised "explosive" new revelations about Washington's surveillance targets, the South China Morning Post reported.

"I'm neither traitor nor hero. I'm an American," Snowden told the Hong Kong newspaper in an exclusive interview, released two days after he checked out of a city hotel and went to ground.

Supporters of the former National Security Agency subcontractor are feting him as a whistleblower for divulging NSA monitoring of private users' web traffic and phone records, in a worldwide trawl that the White House says was needed to keep Americans safe from terror.

The SCMP, in a teaser posted online before it publishes the full interview, said the 29-year-old one-time CIA analyst would offer "more explosive details on US surveillance targets". That will only stoke the anger of those in Washington who accuse Snowden of a rank betrayal.

Snowden would also discuss his fears for his family and his immediate plans, the newspaper said, after it interviewed him earlier Wednesday at a secret location in the semi-autonomous Chinese territory.

"People who think I made a mistake in picking HK as a location misunderstand my intentions. I am not here to hide from justice; I am here to reveal criminality," it quoted him as saying.

Snowden pledged to resist any extradition attempt by the US government, the newspaper said, after he came to Hong Kong on May 20 and leaked the NSA's global eavesdropping operation to the Guardian and the Washington Post.

"My intention is to ask the courts and people of Hong Kong to decide my fate. I have been given no reason to doubt your system," he said.

But, Snowden added, the US government was "trying to bully" Hong Kong authorities into expelling him before he can reveal alleged NSA snooping of communications inside the financial and trading hub.

He also said: "I have not spoken to any of my family. I am worried about the pressure they are feeling from the FBI."

The Justice Department has launched a criminal investigation, but so far the United States has not filed a formal extradition request to Hong Kong, a former British colony that retained its separate legal system when it returned to Chinese rule in 1997.

Ultimately, Beijing retains control over defence and foreign affairs -- and can veto extradition rulings made by Hong Kong courts. The Hong Kong and Chinese governments have yet to make any comment about Snowden.

Hong Kong press reports said that Snowden was on the hunt for representation from prominent lawyers well-versed in human rights and asylum cases.

He is winning support from the city's feisty pro-democracy movement, with a demonstration in the works for Saturday. Organisers said the protesters, set to include Hong Kong lawmakers, would march first to the US consulate and then government headquarters.

"We should protect him. We are calling on the HK government to defend freedom of speech," Tom Grundy, a spokesman for the organisers, told AFP Wednesday.

"We don't know what law he may or may not have broken but if Beijing has a final say, they don't have to extradite him if he is a political dissident," he said.

A protracted battle over Snowden's fate threatens to test new attempts to build US-Sino bridges as shown at a weekend summit in California between the nations' presidents, Barack Obama and Xi Jinping. The European Union has already expressed disquiet at the giant scale of the NSA operation.

White House spokesman Jay Carney on Tuesday said that Obama had signed an executive directive requiring protections for intelligence community whistleblowers who use "appropriate" channels -- implicitly not leaks to newspapers as Snowden did -- to expose alleged wrongdoing.

But Carney fended off all questions about Snowden and declined to characterise his actions while investigations are underway. On Capitol Hill, the language was blunter.

The Republican Speaker of the House of Representatives, John Boehner, described Snowden's leaks as a "giant" violation of law.

"He's a traitor," Boehner told ABC News in an interview. "The disclosure of this information puts Americans at risk. It shows our adversaries what our capabilities are."

The NSA chief, General Keith Alexander, is to testify before a US Senate committee later Wednesday at a pre-arranged hearing at which he is now expected to face questioning about PRISM, the intelligence operation divulged by Snowden.

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