Protestors took to Hong Kong streets on Sunday to march for press freedom, in a demonstration organised by journalists as fears grow that free expression is being compromised.

Organisers estimated 6,000 participated in the march -- though police said the figure was 1,600 -- many wore blue ribbons as a symbol advocating free expression in the media.

There have been mounting concerns that China seeks to tighten control over the semi-autonomous region -- and rein in the press.

"Headlines have been edited, interviews were barred, and columnists were fired. Some see these as commercial decisions or even labour disputes. But we have to see this from the context of tightening control on media in Hong Kong," Shirley Yam, vice-chairwoman of the Hong Kong Journalists Association, told AFP at the rally.

Protesters chanted slogans such as "Free the people. Free Hong Kong. No censorship", as they marched through the streets before arriving at the district of Admiralty where the city's government headquarters are situated.

This month, two international organisations expressed concerns over the status of press freedom in Hong Kong.

The New York-based Committee to Protect Journalists (CPJ) said media freedom in Hong Kong was currently "at a low point", citing self-censorship among reporters, financial and physical threats against the media and legislative steps that could hinder investigative reporting.

Paris-based Reporters Without Borders said Hong Kong's media independence "is now in jeopardy" as China flexes its muscles to stifle critical coverage.

Under a deal between London and Beijing leading to the city's handover in 1997, freedom of the press, among other rights, should be preserved for at least 50 years.

"There has been a worrying trend of rising self-censorship. This is something that affects all journalists," Jonathan Hopfner, a Hong Kong-based journalist and a member of the city's Foreign Correspondents' Club, told AFP at the rally.

"Many media organisations choose Hong Kong as a base because of its strong tradition of free speech. We expect those rights to remain in place," he said.

Martin Lee, former Democratic Party chairman who is among those in rally, told AFP: "When the freedom of the press is gone, no other freedom can be saved."

The city's government, led by pro-Beijing leader Leung Chun-ying, has denied any attempts by the authorities to suppress the press.