Edward Snowden Photo: IC

Edward Snowden, the former National Security Agency (NSA) contractor who blew the whistle on the US government's mass surveillance programs, has been reunited in Russia with his long-time girlfriend, according to a new documentary shown on Friday.

Lindsay Mills, a dancer who was living with Snowden when he left Hawaii for Hong Kong in May 2013, joined him in Moscow in July 2014, the documentary disclosed.

The two are shown cooking together in an apartment in Moscow, where Snowden has been living since he was given asylum and later a three-year residency permit.

Mills had remained silent and her whereabouts were largely unknown after Snowden's release of tens of thousands of classified US intelligence documents in 2013.

Citizenfour, made by US film maker Laura Poitras, who shared a Pulitzer Prize this year for her role in publicizing the Snowden documents, had its world premiere at the New York Film Festival on Friday.

It gives a fly-on-the wall account of Snowden's tense days in a Hong Kong hotel and his encounters with journalists from the Washington Post and Britain's Guardian newspaper as they prepared to divulge details of NSA programs that gathered data from the Internet activities and the phones of millions of ordinary Americans and dozens of world leaders.

Citizenfour takes its title from the e-mail alias that Snowden used when he first approached Poitras in early 2013 through a series of encrypted e-mails with a view to leaking details of the top-secret programs to the media.

Marketed as a "real-life thriller," it is the first of several major films in the works about Snowden, who is wanted by the US on charges brought under the Espionage Act.

"This was a film we had to make as privately and secretly as we could," Poitras said after the screening, which received thunderous applause from an audience that included Snowden's father and other family members.

"We very much wanted to communicate in this film that (it) was about people who take risks and come forward at huge personal sacrifice," added Poitras.

The documentary will open in US movie theaters on October 24.