The former editor-in-chief of prominent Hong Kong newspaper Ming Pao — whose ouster in January sparked protests by many of the paper’s staffers — was stabbed Wednesday morning and has been hospitalized in critical condition, police said.

    The incident prompted an outcry from local journalist groups, with one lumping it in with other threats against journalists in the city in recent months. Meanwhile, Hong Kong’s chief executive, Leung Chun-ying, said he was gravely concerned about the assault.

    Current Ming Pao chief editor Cheung Kin-bor said in an interview that Kevin Lau was in the hospital after being attacked on the street by a knife-wielding assailant on Tai Hong St. in the city’s Sai Wan Ho neighborhood.

    “We still know nothing about the details,” said Mr. Cheung. “We are awaiting reports from the doctor and the police.”

    Police said that they received a call around 10:20 a.m. from a 49-year-old victim, surnamed Lau. According to Mr. Lau, the police said, his assailant was wearing a helmet and attacked him with a knife before jumping onto a motorcycle driven by another driver and speeding away.

    Mr. Lau was taken to the hospital in a conscious state, and police are currently investigating. Attempts to reach Mr. Lau were not successful. The motive behind the incident was unclear.

    Ming Pao’s decision to replace Mr. Lau was met by protests by staffers, who called on the paper to explain the move. Ming Pao has said Mr. Lau’s removal will not change the paper’s editorial direction. Nearly 300 former Ming Pao staffers have also signed a petition expressing their concern about potential threats to Hong Kong’s press freedom.

    Demonstrators rally outside the offices of Chinese language newspaper Ming Pao to protest the replacement of chief editor Kevin Lau, a month prior to his attack. 
    Agence France-Presse/Getty Images

    Mr. Lau’s removal was one factor behind a weekend rally to support press freedom in the former British colony, which organizers said attracted 6,000 people and police said drew some 2,200 at its peak. Earlier this month, the Committee to Protect Journalists also warned that the city’s journalists face increased self-censorship threats as China’s economic sway grows.

    Though Hong Kong returned to Chinese control in 1997, it retains its own independent political, economic and judicial systems under the “one country, two systems” principle governing its relationship with Beijing.

    Hong Kong slipped three places to No. 61 this year in this year’s World Press Freedom Index, annually released by the Paris-based Reporters Without Borders.

    The Hong Kong Journalists Association condemned the attack on Mr. Lau “in the strongest terms” on Wednesday and urged the city to “pursue his attackers and those malignant forces behind them without fear or favor.”

    Mr. Leung, Hong Kong’s chief executive, urged residents with information about the attack to step forward. “We cannot tolerate these kinds of violent incidents,” he said.

    Founded in 1959, Ming Pao is known for its critical reporting on the government. “Ming Pao remains one of the few independent voices in Hong Kong,” said HKJA vice-chair Shirley Yam, citing the fact that the newspaper collaborated with the overseas investigative group ICIJ to produce a series of headline-grabbing reports on the offshore companies maintained by mainland officials.

    “I’ve known Kevin since the 80s. He is such a gentle person—knowing his family background and character, I cannot think of any personal reason why anyone would want to kill him,” said Ms. Yam.

    The Foreign Correspondents’ Club also condemned the attack in a statement and urged the administration to investigate the “growing number of attacks against members of the press,” adding that such crimes threatened to tarnish the city’s reputation as a free and international city.

    The Committee to Protect Journalists has also warned that some reporters face increasing threats of violence.  Last year, unknown perpetrators rammed a car into the gates of media mogul Jimmy Lai’s home, leaving an ax and machete on his driveway. Mr. Lai is the founder of Next Media, a group known for its trademark colorful reporting on everything from celebrity gossip to crime to human rights. Several other employees of the group have also previously been threatened with knife attacks.

    – Te-Ping Chen. Follow her on Twitter @tepingchen.