Brooklyn Borough President Eric Adams appeared to take a tenuous lead in New York City’s Democratic mayoral primary on Tuesday, but it could be weeks before it is clear who is ahead in the city’s first ranked choice voting election.

As voting began on Tuesday, a majority of Democrats ranked Adams as their top choice in the race. It was unclear, however, whether that lead would hold. There were still 207,500 absentee ballots to be counted. The full rankings of the candidates by voters have yet to be considered. In the Democratic primary, a winner may not be declared until July.

Adams, a former police captain who co-founded a Black officers’ leadership group, was leading former city sanitation commissioner Kathryn Garcia and former de Blasio administration lawyer Maya Wiley. Speaking to ecstatic supporters, Adams acknowledged that he had not yet won, and that multiple rounds of ballot counting remained under the ranked choice system.

Former presidential candidate Andrew Yang, who trailed in early returns, conceded about two hours after the polls closed and pledged to work with the next mayor. Curtis Sliwa, the founder of Guardian Angels, defeated businessman Fernando Mateo in the Republican primary. Because there were only two candidates in the race, ranked choice voting was not used.

If elected, several candidates in the race to succeed Mayor Bill de Blasio have the potential to make history. Depending on who wins, the city could get its first female mayor or its second Black mayor.

However, in the Democratic primary, the initial picture may be deceptive. Following the close of polls at 9 p.m., New York City’s Board of Elections began releasing results of in-person votes cast, but the returns focused on who candidates ranked as their first choice.

The ranked choice system, which was approved by referendum for use in New York City primaries and special elections in 2019, allowed voters to rank up to five candidates on their ballot.

The votes are then tabulated in computerized rounds, with the person in last place eliminated each round and ballots cast for that person redistributed to the surviving candidates based on voter rankings. This process is repeated until only two candidates remain. The person who receives the most votes wins.

The Board of Elections will not conduct a tally of those votes using the new system until June 29 It will not include absentee ballots in its analysis until July 6, making any count prior to that date potentially unreliable.

When voters listed their second, third, and fourth choices in the ranked choice voting system, Adams trailed both Garcia and Wiley in the votes counted on election night.

Other Democratic candidates in the race included City Comptroller Scott Stringer, former U.S. Secretary of Housing and Urban Development Shaun Donovan, former Citigroup executive Ray McGuire, and nonprofit executive Dianne Morales.

Stringer, McGuire, and Morales spoke to supporters after the polls closed, despite the fact that early results showed them trailing the front-runners, but they did not immediately concede.

Due to term limits, De Blasio, a Democrat, will leave office at the end of the year. The candidates went on a final round of campaigning in the city on Tuesday.

Concerns about an increase in shootings during the pandemic have dominated the mayoral campaign in recent months, even as candidates have grappled with left-wing demands for more police reform.

Adams may have benefited the most from the policing debate as a former officer, but one who spent his career fighting racism within the department. Both Wiley and Stringer, who are competing for progressive votes, have stated that they will reallocate a portion of the police department’s budget to other city programs.

If elected, either Garcia or Wiley would be the city’s first female mayor. Adams or Wiley would be the city’s second African-American mayor.

Yang and Garcia formed an alliance in the final days of the campaign, ostensibly to use the ranked voting system to defeat Adams. The two held several joint campaign events, with Yang asking his supporters to vote for Garcia as their No. 2 — though Garcia did not reciprocate, refusing to tell her voters where to vote for Yang. Adams accused his two opponents of attempting to deliberately obstruct a Black candidate.