HONG KONG--Chinese state media said Hong Kong schools have become "lawless" as controversy builds over a history question in a school exam, rekindling tensions over academic freedoms in the semi-autonomous city.

Beijing and some Hong Kong officials have frequently flagged the education system as a potential breeding ground for the large-scale, often-violent pro-democracy protests which roiled the city in the second half of last year.

The latest row was sparked over a question on a Diploma of Secondary Education test, which asked students to argue whether Japan had done "more good than harm to China during the period between 1900 and 1945."

A Xinhua commentary published late Friday said Hong Kong schools had failed to 'decolonize' and the territory's education system had not developed in line with the 'one country, two systems' rule.

Hong Kong returned to Chinese rule in 1997 under an agreement with former colonial master Britain that the city would have a high degree of autonomy and enjoy some freedoms unavailable in the mainland.

"The schools seem to have become a lawless place that can unscrupulously promote heresies, attack the 'one country, two systems' and discredit the nation state," Xinhua wrote on its website.

"Some immature students have been tricked into use by the anti-China forces and have become pawns to disrupt Hong Kong."

Hong Kong Education Secretary Kevin Yeung has asked the Hong Kong Examinations and Assessment Authority (HKEAA) to investigate why the question was part of the history exam, sat by 5,200 students, and asked for it to be invalidated.

The question "seriously hurt the feelings and dignity of the Chinese people who suffered great pain during the Japanese invasion of China," Yeung said on Friday.

Public broadcaster RTHK reported on Saturday, citing unnamed sources, that two officials from the HKEAA had resigned following the controversy.

In an interview with pro-Beijing publication Ta Kung Pao, Hong Kong chief executive Carrie Lam said last week the government would examine the future structure of the subject, which is part of the university entrance exams curriculum.

An attempt by the government to introduce "national education" in Hong Kong in 2012 to instill patriotism and promote appreciation of mainland China was met with large protests and scrapped.