One of many poignant tributes to the fallen was held in Trafalgar Square in central London, where an estimated crowd of 5,000 gathered for the Silence in the Square event, hosted by the Royal British Legion.
At 11 a.m. (6 a.m. ET), with chimes from Big Ben
marking the time, traffic surrounding the square -- one of the capital's busiest tourist sites -- came to a halt along with the crowds for a two-minute silence.
A spokeswoman for the British Legion told CNN that motorists turned off their engines and stepped out of their vehicles to stand and show their respect for the fallen.
The event, now in its ninth year, is held to recognize the sacrifices of all generations of the British Armed Forces who have served to defend freedom.
It concluded with members of the crowd placing poppy petals in the Trafalgar Square fountains as a symbolic act of remembrance.
In Bristol, 19,240 shrouded figures were laid out on College Green, next to the cathedral. Each one represented a soldier killed on the first day of the Battle of the Somme on July 1, 1916.
The display was created by Rob Heard, an artist from Somerset. Heard sourced information on the men who fell from the Commonwealth War Graves commission and wrapped and bound each 12-inch figure in a hand-stitched shroud.
"We hope the installation will prompt renewed reflection on events that took place a hundred years ago and on our current experience of war and terror," David Hoyle, dean of Bristol said in a statement on the Bristol Cathedral website.
The shrouds were previously displayed in Exeter to mark the 100-year anniversary of the start of the Battle of the Somme in July. According to the Commonwealth War Graves Commission, by the time the battle ended 141 days later in November 1916, more than 1 million Commonwealth, French and German soldiers had been wounded, captured, or killed.
At the National Memorial Arboretum in Staffordshire, Prince Harry observed the two-minute silence and laid a wreath of poppies. The prince -- a former captain in the British Army who served in Afghanistan -- also gave a reading of Rupert Brooke's poem, "The Soldier."
The annual Armistice Day honors those who lost their lives during times of war. Poppies have been used as a way of commemorating World War I for decades -- in Britain, thousands of paper flowers are sold for charity each year and are worn in people's lapels.
The flowers grew over the battlefields of northern France and Belgium.
In Paris, French President François Hollande attended an Armistice Day ceremony at the Arc de Triomphe, laying a wreath at the foot of the Tomb of the Unknown Soldier.