* Former editor in critical condition after attack in broad daylight
* Assault follows mass protest denouncing intrusions on press freedom
* Incident seen as warning to vibrant journalist community (Recasts with fresh reaction)
By James Pomfret and Alice Woodhouse
HONG KONG, Feb 26 (Reuters) - A former chief editor of a major Hong Kong newspaper known for its critical reporting was stabbed and seriously wounded on Wednesday in an attack that has fuelled concerns about what many see as an erosion of media freedoms.
A man in a helmet attacked Kevin Lau, former chief editor of the Ming Pao daily, in broad daylight on a leafy harbourfront street, slashing him in the back several times. The assailant rode off on a motorcycle with an accomplice.
The attack took place days after 6,000 journalists marched to Hong Kong's government headquarters to demand the city's leaders uphold press freedom against what they see as intrustions from mainland China in a politically sensitive year.
Doctors said Lau's injuries were severe and included a 16-cm (6.5-inch) gash. He remains in a critical condition.
Police said they had so far no clues as to who might have carried out the attack. No one had been detained.
An incident of such brutality is unusual in the former British colony, which reverted to Chinese rule in 1997.
Such an attack, however, aimed at wounding rather than killing, was widely interpreted as a warning to Hong Kong's vibrant media that has remained a bastion of critical reporting on China, a far cry from mainland China, where media are subject to heavy censorship and state control.
The Hong Kong Journalists' Association called on authorities to "pursue his attackers and those malignant forces behind them without fear or favour. The attackers must be brought to justice as quickly as possible to allay public fears."
Media outlets have been subject to attacks. The offices of a small independent media outlet were recently ransacked and a car rammed the front gate of the home of Jimmy Lai, publisher of Hong Kong's anti-Beijing newspaper, the Apple Daily.
In the late 1990s, two prominent media figures, Albert Cheng and Leung Tin-wai, were slashed by men with knives in cases that remain unsolved.
BEIJING RESISTING PRESSURE FOR FULL DEMOCRACY
Hong Kong, a freewheeling capitalist hub, enjoys a high degree of autonomy and freedom. But Beijing's Communist Party leaders have resisted public pressure for full democracy, stoking tensions as the city prepares for a direct vote for its leader in 2017.
Pro-democracy groups have threatened to barricade the city's financial and business center this summer if Beijing does not allow a poll with opposition activists.
Some insiders at Ming Pao said recent exposes on assets hidden offshore by China's elite - in collaboration with the International Consortium of Investigative Journalists (ICIJ) - could have been a factor for the attack.
Lau, a respected Hong Kong-born editor at Ming Pao with a straight-talking style, was recently replaced by a Malaysian Chinese journalist with suspected pro-Beijing leanings, who is expected to take up his duties this week.
Lau's removal to a lesser role in the group sparked a revolt in the Ming Pao newsroom by journalists who suggested the paper's editorial independence might be undermined.
"This attack will damage perceptions of Hong Kong as a safe city and its reputation for media freedoms," said Phyllis Tsang of the Ming Pao Staff Concern Group.
Co-founded by martial arts novelist Louis Cha in the late 1950s, Ming Pao is now owned by a low-key Malaysian media baron with extensive Chinese business interests - Tiong Hiew King - through his Media Chinese International.
Hong Kong's leader, Leung Chun-ying, said the city would not tolerate this kind of "savage attack". Democracy activists denounce Leung as a loyalist to Beijing's Communist leadership.
The U.S. Consulate said in a statement it was "deeply concerned" by the assault. (Additional reporting by Greg Torode; Editing by Ron Popeski)