Australia's tough gun laws have been significantly watered down by state governments since they were introduced under the National Firearms Agreement in the days after the Port Arthur Massacre in 1996, a new study has found.

According to the research by Philip Alpers, an associate professor of public health at the University of Sydney, all Australian states have succumbed to pressure from gun owners or the parties that represent them to water down some aspects of the agreement.

Most notably, he said, most states now allowed children to fire guns, while in NSW and QLD the ban on high-powered semi-automatic weapons of the sought used in the Port Arthur massacre – and commonly in US mass shootings – had been diluted.

Further, the mandatory cooling off period, which dictated that before a person could buy a gun they had to wait 28 days from their application for a license or permit, had been relaxed in most states, Professor Alpers said.