Democratic front-runner Hillary Clinton is appealing to African-American voters to prevent the progress achieved under Barack Obama's presidency from being "torn away" if her Republican counterpart is elected to the White House.

Speaking to thousands at an NAACP dinner in Detroit on Sunday, Clinton pointed to Donald Trump's "insidious" role in the birther movement that questioned Obama's citizenship and his refusal to immediately denounce white supremacist David Duke.

Clinton says "we cannot let Barack Obama's legacy fall into Donald Trump's hands."

The former secretary of state, senator and first lady says "let's not endanger the promise, the potential, the dream of our country by giving in to these voices of hatred."

Clinton says bringing the country together is more urgent than ever with Obama's presidency ending.