For the Port Arthur massacre in Tasmania in 1996, 35 people were killed. This event is usually what is meant by “Port Arthur” in this context.
Port Arthur massacre (Tasmania)
The Port Arthur massacre took place on 28–29 April 1996 in and around the Port Arthur historic site in Tasmania, Australia. During this mass shooting, 35 people were killed and around 18–23 others were wounded, making it the deadliest mass shooting by a single gunman in Australia’s history.
The attacker, Martin Bryant, was later arrested and sentenced to 35 life terms plus additional years, and the scale of the tragedy led directly to major reforms in Australian gun laws under the National Firearms Agreement.