Northam worshipped at his home church, the predominantly black First Baptist in Capeville, but otherwise kept out of sight as calls intensified for him to step down.
Even if Northam doesn't resign, the scandal threatens to cripple his ability to govern. He has lost the support of virtually all of the state's Democratic establishment.
Top Republicans in the Virginia General Assembly also urged Northam to step down, as did many declared and potential Democratic presidential candidates.
Virginia governors can be removed for "malfeasance in office, corruption, neglect of duty, or other high crime or misdemeanor" under the state constitution, but top Democrats said they don't believe it will come to that.
Former Virginia Governor Terry McAuliffe predicted that Northam — who served as McAuliffe's lieutenant governor — will eventually leave office.
"Ralph will do the right thing for the Commonwealth of Virginia," McAuliffe said on CNN's State of the Union.
Northam apologised on Saturday for appearing in the photograph on his yearbook page. He did not say which costume he was wearing, but said he was "deeply sorry for the decision I made to appear as I did in this photo." Yesterday, though, the governor reversed course and said the picture "is definitely not me".
While talking with reporters, Northam admitted he once used shoe polish to put on blackface as part of a Michael Jackson costume for a 1984 dance contest in Texas, when he was in the Army. Northam said he regrets that he didn't understand "the harmful legacy of an action like that".
Asked by a reporter if he could still do Jackson's famous moonwalk, Northam looked at the floor as if thinking about demonstrating it. His wife put a stop to it, telling him, "Inappropriate circumstances".
His shifting explanations did little or nothing to sway prominent Democrats who had swiftly disowned him.
Both of Virginia's US senators, Mark Warner and Tim Kaine, joined the dean of Virginia's congressional delegation, Representative Bobby Scott, in saying they no longer believe Northam can serve effectively. James Ryan, president of the University of Virginia, said in a statement that it would be "exceedingly difficult" for Northam to continue serving.
If Northam does resign, Lieutenant-Governor Justin Fairfax would become the second African-American governor in the state's history. He stopped short of calling for Northam's departure but said he "cannot condone actions" from Northam's past that "suggest a comfort with Virginia's darker history of white supremacy, racial stereotyping and intimidation."
McAuliffe faulted Northam's handling of the furore.
"If it wasn't him in the photo, he should've said that on [Saturday]," McAuliffe said.
"Instinctively, you know if you put black paint on your face. You know if you put a hood on. And so if it isn't you, you come out immediately and say, 'This is not me.'"
Ultimately, McAuliffe said, "It doesn't matter whether he was in the photo or not in the photo at this point. We have to close that chapter. We have to move Virginia forward."
One of the few voices backing Northam was former Virginia Congressman Jim Moran, a Democrat who served in Congress from 1991 to 2015.
Moran told ABC's This Week that Northam's record — including his support of Medicaid expansion and of public schools in minority neighbourhoods — shows that the embattled governor is a friend of African-Americans and that he should ride out the storm.
"I think it is a rush to judgment before we know all of the facts and before we've considered all of the consequences," said Moran, who is white. "I don't think these public shamings really get us all that much."
- AP
