Port Arthur deaths will be remembered: PM

The Port Arthur massacre is a reminder to all Australians just how precious life is, Prime Minister Malcolm Turnbull says.

Twenty years on from the day a lone gunman killed 35 people and wounded 23 others at the historic site, Mr Turnbull and his wife Lucy will on Thursday attend a commemorative service alongside Opposition Leader Bill Shorten and former coalition prime minister John Howard.

"It was a reminder of how precious life is and that's what we'll being remembering today," he told 7HO radio in Hobart.

But while a national tragedy, the events of April 28, 1996 also led to long-lasting change.

Mr Turnbull praised Mr Howard, saying the national firearms agreement he struck following the massacre was one of his greatest achievements as prime minister.

"It has kept Australians safer ever since," Mr Turnbull said.

Mr Shorten said the best of the Australian spirit emerged out of the tragedy.

"We came together as a nation and from our unity we produced gun laws which have served Australians well ever since," he told reporters in Hobart.

"For this we all owe John Howard."