Prime Minister Malcolm Turnbull says Australian and Japanese World War II soldiers were "ferocious in combat and then forgiving", and the two nations have since formed a powerful friendship that pays dividends.

Sunday marks the 75th anniversary of the Japanese bombing of Darwin - the most destructive attack mounted by a foreign power on Australia.

Mr Turnbull praised the reconciliation between the two countries, which have since forged strong economic ties.

Japan has become the Northern Territory's largest trading partner, and Darwin is home to the multi-billion dollar Inpex gas plant - Japan's biggest foreign investment project.

"The fleets of LNG carriers that will be heading north to Japan are just another part of that very strong partnership," Mr Turnbull said.

Mr Turnbull and Opposition Leader Bill Shorten joined dignitaries from Japan and the United States at a memorial service held in Darwin.

Japan Ambassador Sumio Kusaka offered his sincerest condolences for the lives lost and stressed that security alliances with Australia and America remain more important today than ever before.

"We Japanese will never forget that Japan inflicted immeasurable damage and suffering," he said.

"We resolved to never again repeat the tragedy of war."

In 1942, 188 Japanese enemy planes dropped more bombs on Darwin than in the assault on Pearl Harbour 10 weeks earlier.

About 235 people were killed, up to 400 were wounded, 11 ships were sunk and more than 200 raids would follow across northern Australia.

Seventeen years later, a Japanese company was hired to clear the wreckage from Darwin Harbour, which Labor leader Bill Shorten has heralded as a powerful symbol of post-war reconciliation.

"There were protests in Melbourne and Sydney," he said.

"But here, in this special place which is Darwin, people got on with it. The hand of friendship was extended."

NT Chief Minister Michael Gunner noted that more than 260 Japanese airmen and submariners lost their lives in the Top End during the conflict, and some were never found.

"To families back in Japan, do not worry over your ancestors' remains," he said.

"Like the people of Turkey honour and guard our diggers forever at rest in the soil of Gallipoli, so will the people of the Northern Territory honour and guard the Japanese warriors at rest in our warm and blue sea."

Mr Gunner hopes Australia never gets involved in such a war again.

"We must always remember, because in remembering we understand how much we have to lose," he said.