World leaders gathered in Paris on Sunday to mark 100 years since the end of World War I, with French President Emmanuel Macron, German Chancellor Angela Merkel and UN chief Antonio Guterres each warning that rising nationalism again poses a threat to peace.

US President Donald Trump — who prides himself on being called a nationalist — was among around 70 leaders to attend a solemn ceremony at the Arc de Triomphe in the driving rain.

But neither he nor Russian President Vladimir Putin joined other leaders in a symbolic walk up the Champs-Elysees to the monument.

Three topless protesters from radical feminist movement Femen were arrested trying to reach Trump's motorcade, although French Interior Minister Christophe Castaner said his security had “in no way been threatened”.

Paris, the site of repeated militant attacks since 2015, had mobilised some 10,000 police for an event also attended by Canada's Justin Trudeau, Israel's Benjamin Netanyahu and Turkey's President Recep Tayyip Erdogan.

After church bells rang out across France at 11.00 am — exactly a century after the signing of the Armistice — leaders gathered for a ceremony which included a cello performance and readings from letters written by World War I soldiers.

Macron delivered a stinging indictment of nationalism in a 20-minute speech and called on leaders to learn the lessons of the past.

“Nationalism is a betrayal of patriotism,” he said.

“By saying our interests come first and others don't matter we are erasing what makes a nation precious, what makes it live, what makes it great and most importantly of all, its moral values.”

He warned that to dash hopes for peace through “isolation, violence or domination” would “be a mistake for which future generations would rightly find us responsible”.

The service concluded with the bugle call that was played at 11.00 am on November 11, 1918 to signal the end of fighting on the Western Front.

Trump thanked Macron in a tweet for the “beautiful ceremony” before heading to the US military cemetery at Suresnes, west of Paris to pay tribute to America's war dead.

Ceremonies in New Zealand, Australia, India, Hong Kong and Myanmar had launched a day of remembrance services for a conflict that involved millions of troops from colonised countries in Asia and Africa.

“This was a war in which India was not directly involved yet our soldiers fought world over, just for the cause of peace,” Indian Prime Minister Narendra Modi said on Twitter.

“For our tomorrows, they gave their today,” Australian Prime Minister Scott Morrison told people gathered at a ceremony in Canberra.

In London, Prince Charles laid the first wreath of red poppies, Britain's emblem of remembrance, at the nation's annual commemoration ceremony on behalf of his mother Queen Elizabeth II, who watched from a nearby balcony.

German President Frank-Walter Steinmeier became the first German leader to take part in the service, which was also attended by Prime Minister Theresa May.

Return to the 1930s?

After the ceremony, Merkel and UN Secretary-General Guterres gave the opening speeches at a new peace forum in Paris set up by Macron — with both warning that rising nationalism threatens the rules-based international order.

“The concern I have is that blinkered nationalist views may gain ground once again,” Merkel said, warning that people were calling the “European peace project” into question.

Guterres warned of “many parallels with both the start of the twentieth century and the 1930s, giving us grounds to fear that an unpredictable chain of events could ensue”.

The earlier show of unity at the Arc de Triomphe comes at a time of growing tensions between liberals and populists in the EU, as well as between Europe and the US, two years into Trump's “America First” presidency.

Around 1,500 anti-Trump protesters held a demonstration at Republique square in eastern Paris on Sunday, at which the giant “Baby Blimp” balloon depicting Trump as an infant was flown, following previous appearances in London and New York.

“Mr Hate, Leave Europe,” read one banner at the protest.

Trump had snubbed the Peace Forum, instead visiting a military cemetery in the Paris suburbs, a day after coming under heavy fire for cancelling a similar trip due to rain.

Putin meanwhile said he and Trump — at odds over Washington's sanctions and the abandonment of a Cold War-era nuclear treaty — had had a brief but positive conversation during the centenary events.

The Kremlin said earlier that the prospect of a full meeting between the US and Russian presidents had prompted huge international media interest, leading to concern from the French organisers this could overshadow the commemorations.