WASHINGTON - Thousands of marchers gathered on Washington's national mall on Wednesday to commemorate civil rights leader Martin Luther King's famous "I have a dream" speech 50 years ago as activists said his goal of racial harmony remains elusive.

Remarks from President Barack Obama, the first black US president, and bell ringing around the world will mark the moment that King ended his landmark address, which came to symbolize the struggle for equality among blacks and whites in America.

US President Barack Obama speaks during a ceremony marking the 50th anniversary of Martin Luther King Jr.'s "I have a dream" speech on the steps of the Lincoln Memorial in Washington, August 28, 2013. [Photo/Agencies]

Marchers, many wearing T-shirts with King's face on them, began their walk near the US Capitol and carried signs such as "Stop the new Jim Crow" and "Every Texan deserves a vote."

Fighting restrictive voting rights laws that Democrats say hurt minorities, combating joblessness and reducing gun violence among African Americans are among the issues that civil rights leaders put at the forefront of their efforts in 2013.

"This march was supposed to be about jobs, but it's about a lot more," said marcher Ash Mobley, 27, of Washington who said she was there to represent her grandmother, who had been at the 1963 event.

The marchers were led by a line of military veterans and people who had been at the 1963 march, their arms linked. People sang "We Shall Overcome" and other civil rights anthems.

Participants gathered at the Lincoln Memorial, site of King's address on August 28, 1963, for speeches from dignitaries and civil rights leaders.

The ceremony will include bell ringing at 3 PM EDT (1900 GMT), 50 years to the minute after King ended his clarion call of the civil rights movement with the words "Let freedom ring."

About 50 US communities or organizations have said they will ring bells. The Swiss city of Lutry and Tokyo are also taking part, said Atlanta's King Center, one of the event's organizers.

Obama addresses the crowd at 2:45 PM

ECONOMIC GAP PERSISTS

His address commemorating King, a Nobel Peace Prize winner and advocate of non-violence, comes as the White House edges closer to launching military strikes in Syria in response to what US officials believe with certainty was a chemical weapons attack by the Syrian government on civilians.

During a town hall-style meeting last week in Vestal, New York, Obama said the country's history of racial discrimination had contributed to a persistent economic gap between blacks and whites in the decades since King's speech.

Obama, whose mother was white and whose father was black, has sometimes seemed reluctant to weigh in on persistent racial divides in the United States, but he spoke forcefully about the issue last month after the man who killed black Florida teenager Trayvon Martin was acquitted.

The "Let Freedom Ring and Call to Action" ceremony comes as almost half of Americans say much more needs to be done before the color-blind society King envisioned is realized.

Wednesday's event caps a week-long celebration of King's historic call for racial and economic justice. They included a march on Saturday that drew thousands of people urging action on jobs, voting rights and gun violence.

Former Presidents Jimmy Carter and Bill Clinton were also expected to speak.

Former President George W. Bush, who did not attend, said in a statement that the United States has come a long way in civil rights progress but said the "journey to justice" was not complete.

"There's still a need for every American to help hasten the day when Dr. King's vision is made real in every community - when what truly matters is not the color of a person's skin, but the content of their character," Bush said in a statement.

King, a black clergyman, was among six organizers of the 1963 "March on Washington for Jobs and Freedom," where he made his address.

King's speech is credited with helping spur passage of sweeping civil rights laws. A white prison escapee assassinated him in 1968.