Virginia Governor Ralph Northam faced the public today and defiantly said he will not resign because he does not believe that it is him in a racist photograph from his 1984 medical school yearbook.

"I am not either of those people in that photo," Northam, a Democrat, told media gathered at the Executive Mansion, referring to the image of a person dressed in blackface and another in a Ku Klux Klan robe on his yearbook page.

Northam said yesterday was the first time he'd seen the photo, which he called "shocking and horrific."

But he alluded to other actions in his past, and disclosed that in 1984 he won a dance contest in San Antonio where he wore dark shoe polish on his cheeks as part of a Michael Jackson costume.

"I have made mistakes in my past but I am a person of my word, I have great friends on both sides of the aisle," Northam said. "This has been hurtful and that's why I reached out and apologised. . . . I will work hard to maintain their faith in me and my ability to lead and hopefully together we'll move forward."

Northam said if he felt he wasn't able to function efficiently as governor, he would re-visit the matter.

His explanation runs counter to his public apology yesterday, when he acknowledged that he appeared in what he called a "clearly racist" image.

"My first instinct is to reach out and apologise because this was so hurtful. After I did that, I had a chance to reach out to classmates and my roommates and I am convinced, that's not my picture."

The legislative Black Caucus repeated its call for Northam's resignation after his remarks today. "In light of his public admission and apology for his decision to appear in the photo, he has irrevocably lost the faith and trust of the people he was elected to serve," the caucus said in a statement. "Changing his public story today now casts further doubt on his ability to regain that trust."

Tom Perez, chairman of the Democratic National Committee, released a statement that said Northam no longer has the public trust and should step down. "His past actions are completely antithetical to everything the Democratic Party stands for," Perez said. "Virginians and people across the country deserve better from their leaders, and it is clear that Ralph Northam has lost their trust and his ability to govern."

Virginia Governor Ralph Northam, left, gestures as his wife, Pam, listens during a news conference in the Governors Mansion at the Capitol in Richmond. Photo / AP

Northam said he selected three other photos that appear on the page but not the offensive image. He said he didn't purchase the yearbook, and did not know the photo was on his page.

"He should have said that yesterday then," said state Senator Louise Lucas, D, who was among the lawmakers who received a call from Northam today. "He just told me he didn't think it's him. And I said, 'Ralph, this is a day late and a dollar short. It's too late.'"

Two classmates of Northam's at Eastern Virginia Medical School said that they had never seen him in costumes like those that appear in the photo on his yearbook page. However, they were at a loss to explain how a mix-up might have occurred that would result in the racist image being placed on his page in error, because students were responsible for submitting their own photos.

Tobin Naidorf, who also graduated in 1984 and is now a gastroenterologist in Alexandria, Virginia, said he did not recall the exact procedure for submitting photos to the yearbook staff. However, he said he was the only person who could have submitted the family photos that appeared on his own page.

Walter Broadnax's page in the Eastern Virginia yearbook included a photo of his deceased grandmother beneath the heading "These are the people who have helped keep the dream alive."

"Pictures as close as that, I would have had to have chosen those. I can't speak for Ralph, though," said Broadnax, whose entry also included a favourite Langston Hughes poem. He doesn't remember how the yearbook was created or even seeing it once it was published.

Pamela Kopelove, who is credited in the yearbook as its editor, did not respond to repeated calls for comment.

Demonstrators hold signs and chant outside the Governors Mansion in Richmond. Photo / AP

Northam was defying an avalanche of calls to step down from the office he'd assumed not 13 months ago.

The Republican Party of Virginia issued an early call for Northam's resignation, followed by national Democrats, including a host of 2020 contenders.

Every group allied with the governor, from Planned Parenthood to the state Democratic party and Democratic leadership in the General Assembly urged Northam to leave office. The legislative Black Caucus, joined the chorus calling for his resignation after a tense meeting with Northam.

Even home-state champions who regarded him as a dear friend - including immediate predecessor and patron Terry McAuliffe, himself a potential Democratic presidential candidate - said he had to go.

Friends who hoped he could weather the crisis were wondering if he could survive and avoid becoming the first Virginia governor to resign since the US civil war.

More than a dozen protesters braved the frigid air to protest outside the governor's mansion, holding signs such as "Blackface, no place" and "Step down and do Virginia a favor." They chanted "Resign now!"

"There's no question the tide turned," said one ally, who had been briefed by the governor's senior staff.

Northam and his inner circle had been preparing to fight as news of the photograph broke - he issued a written apology, then a video mea culpa. They planned a "reconciliation tour," taking him across the commonwealth to say he was sorry in person, his ally said.

"Then everything changed," the ally said, as national Democrats unleashed a torrent of calls for his resignation.

Northam, 59, released a statement and a video in which he admitted to appearing in the photo, although he did not say which costume he wore.

"I am deeply sorry for the decision I made to appear as I did in this photo and for the hurt that decision caused then and now," he said.

"This behaviour is not in keeping with who I am today and the values I have fought for throughout my career in the military, in medicine, and in public service. But I want to be clear, I understand how this decision shakes Virginians' faith in that commitment."