Nation marks 50th anniversary of John F. Kennedy assassination

— The eternal flame continues to burn at Arlington National Cemetery in Washington, D.C.

Fifty years ago today, President John F. Kennedy was assassinated in Dallas.

The United States is marking the anniversary with a ceremony in the city's Dealey Plaza, and a moment of silence at 12:30 pm (1:30 pm ET), when Kennedy was shot.

Watch a live stream here.

In Washington, President Barack Obama has ordered that flags be lowered at government buildings.

Thousands of people are expected to gather at Dealey Plaza to honor Kennedy's legacy. Iconic images provide a mental snapshot that even half a century later remain haunting.

"There was a bang. We all said, what was that, was that a shot? Then there were two more bangs closer together," said Robert MacNeil, a reporter for NBC News who was assigned to cover Kennedy's visit to Dallas that day.

"I thought some idiot has fired the shots as a demonstration. It was inconceivable to me that the shots would have been directed at Kennedy," said MacNeil.

News of his death halted the nation.

"I was sitting in Latin class a freshman in High School, and this is just seared into your brain," said Carl Jost, who was visiting Dallas for the ceremony.

"This was the first very serious adult incident in my life, and it's been there ever since," said Leonard Schrank, another visitor.

Fifty years later, that moment in history continues to bring people back to the spot that has become a memorial and a museum.

"It's a unique part of American history, you know, terrible, but something to come see," said Ryan Royse.

The assassination and chaos in the moments that followed sent shock-waves across the country and ripped apart the national era of hope Kennedy so famously inspired.

"Not only his charm, his wit, his glamour, his eloquence, but what he helped to instill in America. That sense of hope and purpose and confidence that America could achieve great things," said Dr. Jeffrey Sachs, author of To Move the World, JFK's Quest for Peace.

Now, five decades on, the nation will once again focus on Dealey Plaza to remember and honor the fallen president.

Earlier this week Obama visited Kennedy's grave at Arlington National Cemetery. The JFK Library and Museum in Boston will open a small exhibit of never-before-displayed items from Kennedy's state funeral.

Dallas Morning News - See a page dedicated to Kennedy's achievements as president and what the assassination meant to American politics and history. A special section in Friday's edition of The Dallas Morning News commemorates the life of President John F. Kennedy and the 50th anniversary of his death.

Interactive timeline of the events on Nov. 22, 1963

Guide to television specials on Kennedy assassination anniversary