Hong Kong education officials have blocked some horrific scenes of the 1930s Nanking massacre in China after a video that contained graphic footage of mass murder traumatised children as young as seven when it was aired in classrooms last year.

Now the educational aid on the massacre by Imperial Japanese Army troops in 1937 has been revised by the Education Bureau, although it still contains some scenes of killing, and a warning not to show it to young children has been added.

About a minute of footage that featured scenes of brutality has blacked out and replaced by a voice-over.

“The massacre by the Japanese army in Nanking city was filmed by foreign war reporters at that time. But because it was too bloody and violent, the school, of course, would not broadcast it for everyone to watch,” the voice-over said.

The voice-over also asked youngsters to observe a minute’s silence in memory of those murdered by the invasion forces.

But the revised teaching resources, outlined in a memo to schools, also included other video links that showed images of the killing of the Chinese victims and their internal organs.

“Schools may use the learning and teaching resources listed in the attachment appropriately according to school conditions and students’ grades and levels of awareness,” the memo said.

The bureau asked all primary and secondary schools in the circular to commemorate the 85th anniversary of the slaughter to reinforce national identity.

The circular attached the same controversial video link that showed Japanese atrocities such as the burial of Chinese civilians alive, as well as fields littered with the dead, including babies.

The video was watched last year by primary school pupils and they were said to be horrified by the images.

A Primary Two pupil told the media some of his classmates cried and others refused to watch the video, which contained “scenes of execution and babies”.

Japanese forces invaded Nanking, now Nanjing, on December 13, 1937, and embarked on a killing frenzy.

It is estimated that about 300,000 people, including defenceless women and children, were murdered over about six weeks.

The bureau will hold a commemorative event next month in a primary school and asked schools to send the principal, a teacher and three pupils to to mark the 85th anniversary of the massacre. Secretary for Education Christine Choi Yuk-link will also attend.

Chu Kwok-kung, a lawmaker for the education sector in the Legislative Council and a primary school head, said teachers were professional in editing teaching materials.

But he said some teachers “had too much confidence in the Education Bureau and thought all the materials were safe to use”.

“Teachers’ intelligence is sometimes higher than the bureau’s officials,” he added.

Chu also warned primary schools to use the video links showing brutal killings because pupils would find them disturbing.