HONG KONG (AFP) - The former editor of a liberal Hong Kong newspaper, whose sidelining triggered protests over media freedom and Beijing's influence in the territory, is in a critical condition after being stabbed, authorities said Wednesday.

Kevin Lau, former editor of the Ming Pao newspaper, was attacked in broad daylight by an unknown number of assailants who escaped on a motorbike in the Chai Wan district where the newspaper's headquarters is located, police said.

"He was conscious, but had injuries to his back and was then sent to hospital," a police spokeswoman told AFP. A government spokesman said Lau was in a critical condition.

Lau was replaced in January by a pro-Beijing editor from Malaysia, prompting protests by staff who feared the move was an attempt to stifle the paper's strong track record of investigative reporting.

The attack comes at a time of growing unease over freedom of the press in the southern Chinese city, with mounting concerns that Beijing is seeking to tighten control over the semi-autonomous region.

Protestors took to the streets again on the weekend over what they said was the erosion of press freedom, and earlier this month two reports from international media watchdogs said self-censorship was becoming commonplace.

Media groups, which have raised concern over a series of sackings of high-profile media figures, called on the police to pursue Lau's attackers.

"We strongly condemn violence and urge the police to take action," Hong Kong Journalists Association chairman Sham Yee-lan told AFP.

Lau edited the Ming Pao newspaper for two years but was reassigned in January, spurring criticism from staff members at a paper celebrated for its investigative journalism and analysis.

Some suspected Lau's sidelining was politically motivated as the city undergoes a key debate over the future of a political system that was subject to numerous investigations under his leadership.

Top Hong Kong officials condemned the attack on Lau.

The territory's Chief Secretary Carrie Lam told reporters that she was "shocked and saddened" by the assault.

"Hong Kong is a city with rule of law. All of society should condemn violence," she said.

Hong Kong was returned from Britain to China in 1997 under a "One Country Two Systems" arrangement that enshrined the right to press freedom among other guarantees.