Services of commemoration are being held around the world to mark the end of World War I in 1918, BBC reported.
Angela Merkel has become the first German chancellor to mark Armistice Day by attending the main French commemorative event in Paris.
In London, the Queen, politicians and armed forces chiefs are marking the passing of the WWI generation.
Later, the US will observe Veterans Day, with President Barack Obama due at a wreath-laying ceremony.
French President Nicolas Sarkozy and the German chancellor rekindled the flame on the tomb of the unknown soldier at the foot of the Arc de Triomphe in Paris, in a symbolic move designed to signal a new era in Franco-German relations.
The two leaders also observed a silence, flanked by soldiers from a Franco-German brigade and officers from both countries' armed forces.
They were reunited just two days after both played a prominent role in the events marking the 20th anniversary of the fall of the Berlin Wall.
Speaking after the formal ceremonies, Mr Sarkozy told Mrs Merkel: "Your presence among us on this November 11th is a gesture of exceptional friendship - every French person knows how significant it is."
Mrs Merkel responded: "Both dates, the end of the First World War, and the day of the fall of the Berlin Wall, remind us that we must always fight for the invaluable goods of peace and freedom, that we need to defend our values, of democracy and human rights, and that we keep working for European solidarity and partnership with America. That is our task."
The memorial service in London, at Westminster Abbey, is being held following the deaths this year of the final three veterans of the war living in the UK.
The Queen led the country in observing a two-minute silence at 1100 GMT for the "passing of a generation". The last three surviving WWI veterans in the UK died this year - Bill Stone died at age 108 in January, followed by both Henry Allingham, 113, and Harry Patch, 111, in July.
At the main UK military base in Afghanistan, Camp Bastion in Helmand province, a padre led prayers for the dead and injured in all conflicts since World War I.
The BBC's Adam Mynott reports that a heavy gun was fired, and for two minutes those who could stood still in silence to pay respects for those killed in war.
He added that at the forefront of people's minds were the 233 British service personnel who had died in Afghanistan since military operations began in 2001.
Australia's east coast, which is 11 hours ahead of GMT, was one of the first places to commemorate the 11th hour of the 11th day of the 11th month - the time the guns of World War I fell silent.
The names of five Australian soldiers killed in Afghanistan since Remembrance Day last year were being added to the roll of honour at the Australian War Memorial in the capital, Canberra, Australian television reported.