Hong Kong police were on Thursday investigating an attack on a former newspaper editor who is in a critical condition after being hacked with a cleaver, the latest incident to stoke fears over media freedom in the territory.

The attack on Kevin Lau, former editor of the liberal Ming Pao newspaper, has sparked condemnation from the US and press groups at a time of growing unease over media rights in the southern Chinese city.

"Officers are now at the scene and they are investigating," a police spokeswoman told AFP.

Lau, who was known for his hard-hitting political investigations, was attacked on Wednesday by two men who escaped on a motorbike in the Chai Wan district where the newspaper's headquarters are located.

"From initial investigations, it is believed that the motorcycle was stolen," the police spokeswoman said.

The journalist has undergone surgeries for wounds including a 16 centimetre-long (six-inch) gash that cut through his back muscles and remains in "a critical condition", a Hong Kong Hospital Authority spokesman told AFP Thursday morning.

Hong Kong chief executive Leung Chun-ying later told reporters "Mr. Lau's situation has made progress", without elaborating on his condition.

The police have described the attack as "a classic triad hit, which was designed to maim, not kill, to send a warning", the South China Morning Post reported.

Security camera images released by police late Wednesday showed two people, believed to be the suspects, wearing dark clothing and riding a motorcycle on a busy street.

On Thursday investigators visited shops and restaurants in the neighbourhood where the attack took place to seek clues, but no arrests have been made so far.


Outrage over attack


The attack on Lau has triggered widespread condemnation, with the US consulate saying Wednesday it was "deeply concerned about... this vicious crime" as it joined calls from media groups for the authorities to bring the perpetrators to justice.

The International Consortium of Investigative Journalists, behind a recent expose on the offshore accounts of China's elites on which it worked with papers including Ming Pao, said it was "horrified" by the assault.

"There is simply no justification for such an attack and it should provoke outrage in all fair-minded citizens," said the group director Gerard Ryle in a statement.

The brutal attack on Lau has made headlines in papers across Hong Kong with Ming Pao's usual red logo coloured black on Thursday.

"My colleagues won't be scared because of this incident, we will continue with our work," wrote the newspaper's interim chief editor Cheung Kin-por.

The assault on Lau comes at a time of mounting concerns that Beijing is seeking to tighten control over the semi-autonomous region.

Lau was removed as editor in January, triggering protests over media freedoms. He still works at the paper in a different role.

The Apple Daily, a popular tabloid critical of Beijing, described Lau as a journalist who steers clear of personal scandals.

The attack on Lau is the latest in a series against journalists in the territory.

In June last year there were multiple attacks against employees of Apple Daily, and Chen Ping -- a publisher of a magazine known for its outspoken coverage of mainland issues -- was also beaten up.