"Gentlemen, we are truly humbled by your presence today," he told the veterans. "Omaha - Normandy - this was democracy's beachhead. And our victory in that war decided not just a century, but shaped the security and well-being of all posterity." After his speech, Obama warmly embraced a stooped veteran barely half his height before bowing his head with France's President Francois Hollande in front of a wreath commemorating the thousands that fell on June 6, 1944.

The two leaders then stood, hand on heart, with saluting veterans standing to attention behind them as a lone bugler sounded out and and jets took part in a fly-past.

For his part, Hollande said France would "never forget what it owes the United States".

"This day, which began in chaos and fire, would end in blood and tears, tears and pain, tears and joy at the end of 24 hours that changed the world and forever marked Normandy," he said.

Britain's Queen Elizabeth led a service at Bayeux cemetery where nearly 5,000 Commonwealth troops are buried.

Not many of the 150,000 Allied soldiers who slogged onto storm-torn beaches or parachuted into Normandy remain alive to pass on the legacy of that "longest day". More than 1,000 of them mingled with 19 world leaders and many others gathered at the day of ceremonies on the beaches of northern France, where the biggest amphibious assault in history was launched.

Sombre and proud, some rose to their feet with difficulty, to the applause of thousands of onlookers, as they paid tribute alongside Obama and Hollande.

At 6.30am, the moment on June 6, 1944, when Allied troops first waded ashore, a US military band sounded their bugles. D-Day veterans from the 29th Infantry Division and serving soldiers stood at attention.

"Twenty-nine, let's go!" they shouted, then downed shots of Calvados, Normandy's apple brandy.

Hundreds of Normandy residents and other onlookers applauded, then formed a human chain on the beach.

One British veteran, 89-year-old Ken Godfrey, was applauded by well-wishers who shouted "bravo" and "thank you" as, medals clinking on his chest, he walked the 1.5km-long path to Bayeux cemetery.

"My main memory is wading through the sea with water up to my chest," he said. "But I don't like to talk about the fighting. If people ask, I just say we had a hairy time. But I'm lucky that I survived."

Bob Cowper, a wheelchair-bound Australian night fighter pilot - who flew over the beaches on D-Day as the fighting raged below - remembered "feeling empathy for all the poor buggers fighting on the ground".

It was Cowper's first trip back to the beaches. "It's wonderful as on old man of 91 - it's like coming home," he said.

D-Day veterans parachute in again

D-Day veteran Jock Hutton, 89, jumped from a plane at 1,500 metres in his own act of commemoration for the 70th anniversary.

The Scot landed in the same field outside the Normandy village of Ranville where, as a member of the 13th Battalion of Britain's Parachute Regiment, he was part of the first wave of troops taking part in the Allied invasion of continental Europe. He said: "At my age, life tends to get a wee bit boring. So you've got to grab at any chance at excitement."

In a concession to his advanced age, the skydive was done in tandem with a member of the Red Devils, Colour Sergeant Billy Blanchard.

But Thursday's jump was 10 times higher than the one he made 70 years ago, aged just 19. He said: "We dropped very low [on D-Day]. We didn't have as much time in the air as we did just then. We smashed into the ground ... my tailbone is now my collarbone!"

The pair touched down on the grass just in front of Prince Charles, who waited for the veteran to dust himself off before shaking his hand. As colonel-in-chief of the Parachute Regiment, the heir to the British throne led the tributes on Thursday to those who made the first air landings just after midnight on June 6.

Walking away from the drop zone, Hutton spotted an old comrade, Bert Marsh, also 89. They met a decade ago at commemorative events in the Ardennes, where both fought.

"Bertie, you old beast. I thought you were dead," said Hutton as they embraced.