The crime-scene footage, which showed close-up images of the victims, was overlayed with text questioning the guilt of Martin Bryant, who was convicted of murdering 35 people during his killing spree in 1996.

The footage was removed from YouTube but a copy uploaded by a different user remains on the video-sharing website. It is not clear when the footage was uploaded or taken down.

A spokeswoman for Google, which owns YouTube, said the company was not able to comment on individual videos or users, but that footage showing harmful and dangerous conduct would violate its terms of usage.

"We regularly remove videos that violate our [terms of usage] from the site after being flagged by the community."

The re-posted video could be flagged by anyone viewing the video as a breach of the terms.

The posting of the video, which was first reported by The Mercury in Tasmania, provoked a furious response from Tasmania Police, who demanded that it be pulled down.

"Unfortunately this isn't the first time that this training video has turned up in the wider community," Deputy Commissioner Scott Tilyard from Tasmania Police told the Telegraph yesterday.

"It has been known for some years that copies of the police training video have found their way into the public domain. A copy was located at a public tip in 2004 which led to an investigation."

He added in a statement this morning: "It is highly distressing not only for the families of the victims, but for the community, for these images to be available on the internet."

Deputy Commissioner Tilyard said this was not the first time the footage had been uploaded on to the internet.

In 2004, a 22-minute film marked as a Tasmania Police Training Video was sold at a Hobart tip shop for 10 cents.

Police said then that a full investigation into how the footage was leaked would be conducted.

Deputy Commissioner Tilyard said the training video was used in the late 1990s by police across Australia and internationally for officers unfamiliar with the scale and nature of the murders.

He said that, during the 1990s before YouTube and other social networking sites existed, "it was not envisaged that these types of videos, if they did fall into the wrong hands, could be circulated so quickly and easily through more modern technologies".

He added that security arrangements around Port Arthur-related material had since been made more stringent.

Deputy Commissioner Tilyard said investigators were working to find out the source of the new postings.

Bryant was jailed for life without parole for the killings on April 28, 1996.

The revelation of the online footage came after the attacks in Norway, in which 76 people were killed at the weekend.

Norwegian Anders Behring Breivik confessed to the killings but has denied guilt.