In the humid pre-dawn light across Southeast Asia thousands will gather Tuesday at memorials marking Anzac Day.
But Australian officials say Vietnam have refused to lift a ban on official memorials at the Long Tan Cross in Vung Tau province, extending a policy in place since August last year.
The ban took effect hours before a planned 50th anniversary commemoration last August was to proceed.
An Australian consular website notice said Vietnam had refused permission for official commemorations at the Long Tan site, including Anzac Day 2017. But "small groups" for "low key" private visits, and without media coverage would be allowed.
At the 1966 battle of Long Tan vastly outnumbered Australian troops fought off an attack by Communist Vietcong.
Vietnamese officials were critical of Australians at last year's Anzac Day ceremonies when up to 1000 people went to the Long Tan site.
Defence analyst Carl Thayer, at the University of NSW, said reports of Australians' behaviour and large crowd "exceeded past understandings" with the Vietnamese who were "very finicky on breaking protocol".
Elsewhere, services would take place at lawn cemeteries and Australian and New Zealand embassies throughout the region.
In Thailand, former Australian prisoners of war Harold Martin, 100 years old this year, and 94-year-old Neil MacPherson, are joining up to 1000 people in the pre-dawn service at the memorial along the World War II Death Railway site of Konyu Cutting, known as Hell Fire Pass. Both men worked on the rail line during the war.
The brutal conditions, starvation and disease claimed the lives of more than 12,600 PoWs, including 2800 Australians, as well as 90,000 Asian labourers forced to work on the line construction between Thailand and Burma.
Mick Clarke, manager of the Australia government-funded Hell Fire Pass Memorial Museum, said visitors, especially younger generation, were shocked by the cruelty faced by the PoWs.
"They try to imagine what the PoWs went through," Clarke told AAP.
In Singapore, memorial services are at the Kranji War Memorial lawn cemetery where thousands of Australians suffered in the notorious Changi PoW camp. Many PoWs from Changi were transported to Thailand to work on the Death Railway.
In Malaysia, the focus of services is Sabah State's Sandakan war memorial built on the site of the PoW camp during World War II.
The ceremonies mark the remembrance of the more than 2430 Australian and British PoWs and local people who perished under the Japanese Imperial rule.
Sandakan was also the site of the notorious march at war's end in 1945 when 1005 PoWs perished from malnutrition or were murdered.
Other services are to take place in the Philippines, Myanmar, Laos and Kuala Lumpur.
Martin Stuart-Fox, emeritus professor of history from Queensland University, said conflicts were called by politicians, but the suffering was borne by ordinary people.
"We sent people out there to fight wars wherever it is and they fought them to the best of their ability and they were our representatives in doing so and we should honour that," Stuart-Fox told AAP.
"These occasions should be celebrations of the discipline and the courage and the honour of those who were thrown into the fight."