Thousands of people endured the rain and cold in downtown Dallas to mark the exact moments 50 years ago when President John F. Kennedy was shot dead.
A sombre tolling of bells and started the ceremony, before those assembled observed a minute silence, followed by a rendition of "America the Beautiful."
Bishop Kevin K. Farrell, of the the Catholic Dioceses of Dallas, speaking at the Commemoration of the assassination of JFK, said that the city had "suffered" following the shooting that had "shock and horrified" the nation.
He said: "Today we lift up our hearts and minds... from the horrible tragedy enacted in this place. From the cruel suffering that was born on this hill.
"From the shock and horror that gripped our nation, and from the years when we, as citizens of this city, suffered and were implicated by the gun shot by one man, that killed a President, in whom many of us had set our hopes and dreams for a better America."
Members of the Kennedy family and mourners have laid a wreath and red roses on the grave of the JFK as memorial services marking the 50th anniversary of the President take place across America.
Two bagpipers marked the start of the solemn memorial at Kennedy's grave in Arlington Cemetery in Virginia this morning.
Members of the Kennedy family laid red roses on the gravesite, which is also the final resting place of his wife Jacqueline and two of their children.
Images of the memorial service in Surrey commemorating the assassination of John F Kennedy have been tweeted by the American ambassador to Britain.
In his tweets, Matthew Barzun said President Kennedy's legacy was "the antidote to cynicism or doubt" and encouraged supporters to "keep conviction and hope alive in his honour".
He praised Britain's "generosity" for building the 1965 memorial, which he described as "a part of England that will be forever America".
Britain has marked the death of JFK with a simple wreath-laying ceremony at the President Kennedy memorial in Runnymede.
Kennedy's granddaughter Tatiana and American ambassador Barzun planted an oak sapling in memory of the fallen President, who was shot and killed shot in Dallas, Texas, on 22 November 1963.
David Cameron has paid tribute to the US President John F Kennedy on the eve of the 50th anniversary of his assassination. He said the thoughts of Britain are with the American people as they prepare to mark the day.
"Wherever you go in the world today, the three letters 'JFK' are instantly recognisable. They summon up the very best of politics: energy, optimism, hope - the belief that a nation united can achieve almost anything," the Prime Minister said.
Tomorrow (Friday) marks half a century since the shooting of JFK in Dallas, Texas - an event which resonates to this day and has spawned numerous conspiracy theories.
"It was these ideals which came to define the Kennedy presidency. He demanded that his country rise to the challenges of its time - and the people responded in kind," Mr Cameron said.
A John F Kennedy enthusiast from the Midlands is flying out to Dallas ahead of the 50th anniversary of the assassination of the former US President.
Patrick Silke has been a keen collector and enthusiast since he took on a project on the subject of the assassination at school, aged 16.
He has amassed dozens of books, magazines, photographs and other memorabilia on the Kennedy family and the story of the assassination of John F Kennedy in particular.
Tomorrow (Friday) marks the 50th anniversary of that assassination, when Lee Harvey Oswald shot the 35th US President, while he was travelling in a motorcade in Dallas, Texas.