A history exam question asking Hong Kong students to assess colonial Japan's occupation of China sparked a rebuke by Beijing on Friday and reignited a row over academic freedoms in the semi-autonomous city.

The criticism comes as Hong Kong's schools and universities -- some of the best in Asia -- become the latest ideological battleground in a city convulsed by political unrest.

China's foreign ministry and state media rounded on a university entrance exam question that asked students whether they agreed Japan "did more good than harm" to China from 1900 to 1945.

"Hong Kong's education sector must not become a chicken coop without a roof," the foreign ministry wrote on the Facebook page of its Hong Kong office, using a metaphor referring to the idea that students should be protected from negative influences or ideas.

"Hong Kong's (university exam) question leads students to be traitors," wrote the pugnaciously nationalist Global Times newspaper on Friday.

After the criticism from the mainland, Hong Kong's Education Secretary Kevin Yeung announced the question would not be marked by examiners because it was "biased" and had "seriously hurt the feelings and dignity of the Chinese people".

He also ordered the city's exam board to report to him on how it was included in the test.

Japan's colonial occupation of parts of China between 1900-1945 was brutal and led to millions of deaths.

Mainland China's schools and universities are strictly controlled, with little deviation from Communist Party lines tolerated.

Semi-autonomous Hong Kong has a much freer system that encourages debate and analysis.

Beijing wants Hong Kong's education system to be more patriotic as calls for democracy in the city grow
Beijing wants Hong Kong's education system to be more patriotic as calls for democracy in the city grow AFP / Anthony WALLACE

But education is becoming a new target for Beijing after seven months of huge and often violent democracy protests rocked Hong Kong last year.

The "chicken coop" metaphor was used by Hong Kong's pro-Beijing leader Carrie Lam last week as she warned liberal studies, a secondary school class that teaches critical thinking, helped fuel last year's unrest.

The subject has become a bete noire for China and pro-Beijing politicians in Hong Kong who have called for more openly patriotic education.

Lam has promised to unveil plans to reform the subject later in the year.

The exam question went viral on China's heavily policed Twitter-like platform Weibo on Friday, with a hashtag about the topic receiving around 400 million views with many comments condemning Hong Kong.

Some academics and teachers are rattled by the government's enthusiasm for reforming curriculums.

Hong Kong Professional Teachers' Union on Thursday accused the government of "placing politics above education".

"In order to pursue political correctness, the education bureau is smothering the space for discussion in exams," the union said.

Ip Kin-yuen, a lawmaker who represents the education sector, said students would be expected to know and write about Japan's violent excesses in an exam question assessing the country's legacy within China.

"Students... can use what they know to discuss against a statement, this is very common in a history exam," he told AFP.

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