Graduating seniors at Bethune-Cookman University turned their backs in protest against US Education Secretary Betsy DeVos at the start of her commencement speech at the historically black institution.

Some graduating students shouted "Liar!" and "Just go," as she powered through her speech on Wednesday at the Florida university.

"Let's choose to hear one another out," DeVos said, reading her prepared text in a measured tone despite continuing waves of boos, catcalls and scattered applause.

As the crowd kept trying to shout her down, university president Edison Jackson briefly took over the microphone to sternly lecture the class of 2017.

"If this behaviour continues, your degrees will be mailed to you. Choose which way you want to go," Jackson warned.

DeVos alienated many African-Americans in February when she described historically black colleges as "real pioneers when it comes to school choice".

After a storm of criticism, she acknowledged that these colleges were "born, not out of mere choice, but out of necessity, in the face of racism".

Betsy DeVos got loudly booed by students at a historically black college. pic.twitter.com/gobykJkzY6 — AJ+ (@ajplus) May 11, 2017

In her keynote, DeVos repeatedly praised the school's founder, Mary McLeod Bethune, as someone who "refused to accept systemic and repulsive racism," and had "the courage to change old ideas".

"I am here to demonstrate in the most direct way possible that I and the administration are fully committed to your success and to the success of every student across this great country," she said.

President Donald Trump's nomination of DeVos, a Republican fundraiser with no classroom experience, was so controversial that Vice President Mike Pence had to cast a tie-breaking vote for her Senate confirmation.

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Some leaders of historically black colleges and universities later expressed dismay when Trump invited them to the Oval Office for a "listening session" that became an apparent photo-op for Black History Month.

DeVos has continued since then to cite historically black colleges as examples of alternative options for quality education, her stated goal for promoting the diversion of tax money from public schools to private companies and charters.

Ahead of the speech, students, alumni and political activists sought to have DeVos' invitation rescinded, saying they were offended by her earlier comment.

About 60,000 signatures on two petitions were delivered to school officials on Tuesday objecting to her appearance at the university.

“Right now is not the time for Secretary DeVos to speak at any historically black college," said Dominik Whitehead, a Bethune-Cookman alumnus who led one of the petition drives.

DeVos' statement, he said, "just shows she is out of touch".

Before the address, activists lined a sidewalk. One sign said, "DeVos is not worthy."

Jackson had been accused of selling out the school by inviting DeVos. He gave her a hug, then took back the podium as she left the stage.

"As we have said repeatedly, be careful of the people you let in your place," Jackson said, seeming to acknowledge the criticism.

But he said "Bethune-Cookman University can't do it alone. We need everyone to be a part of this continuation of our institution."

Some students agreed with Jackson, that the school needs help from anyone offering it no matter their party affiliation.

"DeVos was here to hear our differences and at the end of the day I think that's what happened," said Keith Holt, who received a masters degree in transformative leadership.