Hundreds of people marched to the US consulate on Saturday in support of Edward Snowden, an American citizen who leaked top-secret information about US surveillance programs.

Snowden, who worked as a contract employee at the National Security Agency, revealed to The Guardian newspaper the existence of secret surveillance programs that gathered Americans' phone records and other data.

He is believed to be in Hong Kong.

The 29-year-old American has yet to be publicly charged with any crime and no known warrants have been issued for his arrest.

Protesters braved the rain on Saturday and marched to the US Consulate in Hong Kong to show their support for Snowden.

Some held placards reading "Betray Snowden. Betray Freedom" as they walked.

They also chanted pro-Snowden slogans when they gathered at the rear of the US Consulate.

Claudia Mo, one of the demonstration organisers believes governments "can't claim national security as the umbrella excuse" for monitoring people's lives.

Two protesters from New York also expressed support for Snowden.

"I think Snowden absolutely did the right thing. He had insider knowledge of these surveillance programs, and I think at a great personal risk he was willing to expose this to the world. I don't think he would benefit from this in any way," said Drew Gibson.

"Ultimately it's hard to see how NSA (National Security Agency) spying could be justified legally or morally," said Joseph Gualtieri.

In an interview with the South China Morning Post, Hong Kong's main English-language newspaper on Wednesday, Snowden alleged that the US National Security Agency hacked 61,000 targets, including hundreds in Hong Kong and mainland China.