New York City’s first attempt at ranked-choice voting system plunged into confusion after election officials retracted their latest report on vote count after what it called a “discrepancy”.

That data had indicated that Brooklyn Borough President Eric Adams, a former police captain who would be the city’s second Black mayor, had lost much of his lead and was ahead of former sanitation commissioner Kathryn Garcia by fewer than 16,000 votes.

Then the Board of Elections tweeted that it was aware of “a discrepancy” in its report on ranked-choice voting results but didn’t initially explain what that discrepancy was.

Just before 10:30 pm it released a statement saying that 135,000 ballot images it had put into its computer system for testing purposes had never been cleared.

“The Board apologizes for the error and has taken immediate measures to ensure the most accurate up to date results are reported,” it said in a statement.

Adams’ campaign, which had publicly pointed out the vote discrepancy shortly after the faulty count was released, said in a statement that it remained confident he would ultimately prevail.

The publicized vote totals had included an unexpected jump in the number of ballots counted on Tuesday compared to the number counted on the day of the primary.

Garcia said in a late afternoon news conference, before the numbers were withdrawn, that she was confident she had a path to victory, but wasn’t “counting any chickens before they’ve hatched.”

Later, her campaign issued a statement saying it was monitoring the situation.

“We encourage all New Yorkers to be patient and we hope when an update comes it includes a transparent explanation of the process,” it said.

Elections officials had planned on conducting another round of ranked choice analysis on 6 July that would include absentee ballots.

Since no candidate was the first choice of more than 50 per cent of voters, a computer on Tuesday tabulated ballots in a series of rounds that worked like instant run-offs.

In each round, the candidate in last place was eliminated. Votes cast for that person were then redistributed to the surviving candidates, based on whoever voters put next on their ranking list. That process repeated until only two candidates were left.

Besides Adams and Garcia, civil rights lawyer Maya Wiley was also still within striking distance of victory.

Primary results showed Adams had a lead of around 75,000 votes over Wiley with Garcia close behind in third.

Either Adams or Wiley would be the second Black mayor of New York City, and either Garcia or Wiley would be the first woman mayor.