Other world leaders will join them in Portsmouth for Britain's national event to commemorate the Allied invasion of the Normandy beaches -- one of the turning points of World War II.

Trump, Queen Elizabeth and British Prime Minister Theresa May will be joined by Canadian PM Justin Trudeau, French President Emmanuel Macron and German Chancellor Angela Merkel for an event with the veterans, the youngest of whom are now in their 90s, marking the boats' departure on the eve of the battle.

It will be the last act of Trump's three-day state visit to Britain.

Portsmouth was the main departure point for the largest amphibious assault in history, when some 156,000 US, British, Canadian and other Allied troops sailed for the beaches of northern France.

The Battle of Normandy on June 6, 1944 led to the liberation of Europe and helped bring about the end of World War II.

Proclamation

In a joint D-Day proclamation marking the anniversary, the 16 nations attending Wednesday's ceremony affirmed their shared responsibility to ensure that the horrors of World War II are never repeated.

"Over the last 75 years, our nations have stood up for peace in Europe and globally, for democracy, tolerance and the rule of law," it said.

"We re-commit today to those shared values because they support the stability and prosperity of our nations and our people. We will work together as allies and friends to defend these freedoms whenever they are threatened."

The statement committed to resolving international tensions peacefully.

"In this way, we salute the surviving veterans of D-Day and we honour the memories of those who came before us."

The ceremony is the first time that so many world leaders have gathered in Britain since the London 2012 Olympics.

The prime ministers of Australia, Belgium, the Czech Republic, Luxembourg, the Netherlands, Norway, Poland, the president of Greece, New Zealand's governor-general, Slovakia's deputy PM and the Danish ambassador are due to attend.

Tragic letter

The event on Southsea Common includes an hour-long production recounting the story of the invasion with testimony from veterans, theatrical performances and live music, as well as a flypast.

Some 4,000 military personnel, 26 British military aircraft and 11 British naval vessels will participate.

In the event's official programme, Queen Elizabeth, 93, said: "I am sure that these commemorations will provide an opportunity to honour those who made extraordinary sacrifices to secure freedom in Europe. They must never be forgotten."

May will read a letter written by Captain Norman Skinner to his wife Gladys on June 3, 1944.

The letter was in the British soldier's pocket when he landed on Sword Beach in Normandy on June 6. He was killed the next day.

May will attend a reception with veterans and a lunch with world leaders.

She will call for continued Western unity in tackling the world's security threats.

"Their solidarity and determination in the defence of our freedom remains a lesson to us all," she was to say.

Trump wraps up visit

The D-Day commemorations are among May's last official duties before she steps down as leader of the governing Conservative Party on Friday.

That will trigger a leadership contest. The winner, chosen from 11 candidates, will become the next prime minister by the end of July.

Trump said Tuesday that the D-Day troops stormed the beaches to ensure that their people would forever remain sovereign and free.

"Let us renew our pledge... that the cause for which they died shall live," he said.

The state visit saw Trump join the royal family for a lavish state banquet, while the president promised Britain a "phenomenal" post-Brexit trade deal.

After Queen Elizabeth formally bids him farewell, Trump is off to his golf resort in Ireland before heading to further D-Day commemorations in Normandy on Thursday.

The village of Doonbeg on Ireland's west coast has been decked out in US flags to welcome Trump.