Oprah Winfrey commemorated King's legacy at the 50th anniversary of the March on Washington. (The Washington Post)

Oprah Winfrey encouraged a crowd gathered to commemorate the 50th anniversary of the March on Washington Wednesday to reflect upon the accomplishments of Martin Luther King Jr. and also look ahead to what still needs to be done to realize King's vision.

"As the bells of freedom ring today, we're hoping that it's a time for all of us to reflect not only the progress that's been made -- and we've made a lot -- but of what we've accomplished and also the work that still remains before us," she said.

Nearly 300 sites across the nation will ring bells to commemorate King’s "I Have a Dream" speech.

"He's the one who reminded us that we will never walk alone," Winfrey said.

Latest Updates: The March on Washington’s 50th anniversary