At a ceremony with Vietnamese officials, a small team of Australian veterans shared a database including map references showing where 3,800 Vietnamese are believed to be buried after fights with Australian and New Zealand forces.

"Basically it was the right thing to do," said team leader Bob Hall, a Vietnam veteran and researcher at the University of New South Wales who led the project.

In total some 200,000 North Vietnamese and Viet Cong soldiers who fought in the Vietnam War remain missing -- buried individually or in groups in unmarked graves in the jungle and fields across southern Vietnam, Laos and Cambodia.

Collectively they are known as the "wandering souls" -- from the Vietnamese belief that souls of those improperly buried will continue to wander.

Data in the US National Archives lists 37,000 actions that could have killed around 155,000 people -- including infamous battles at Khe Sanh and Hamburger Hill.

But many more were killed in smaller firefights in remote locations across Vietnam.

Hall said his research -- backed by the Australian Defence Force -- revealed data on every fight involving Australian and New Zealand soldiers in their area of operations in Phuoc Tuy Province.

"Standard operating procedures for Australians was to bury the enemy bodies at the scene. While that was happening, usually the patrol commander was writing a report about what had happened," he told AFP.

"It's those reports that have given us the data we have put into this database," he said, adding they were accurate to around 100 metres.

"I was one of those patrol commanders and I thought at the time the process of writing all this down was pretty much a waste of time. Here I am years later."

The move is part of a broader rapprochement between the Cold War foes. Vietnam has helped Australia recover and repatriate six of its military personnel missing in action.

Last month Scott Morrison became the first Australian prime minister to visit Vietnam in 25 years.

The database was welcomed by the Vietnamese delegation visiting Canberra.

"Family of those soldiers are looking to the information for their loved ones' destiny," said Major General Tran Quoc Dung.

The project, he said, had "contributed significantly to the promotion of the relationship between the two countries in general and the defence relations between Vietnam and Australia in particular".