Obama leads tributes to Martin Luther King

President Obama has led the tributes to Martin Luther King, exactly 50 years since his legendary "I have a dream" speech.

US president Barack Obama has led civil rights pioneers in a ceremony marking the 50th anniversary of the March on Washington, where Martin Luther King’s “I Have a Dream” speech roused the 250,000 people who rallied there for racial equality.

Large crowds gathered at the Lincoln Memorial in the capital to hear the first black US president speak.