The Senate contest between incumbent Republican U.S. Sen. Susan Collins and Democratic Maine House Speaker Sara Gideon was still too close to call on Tuesday night.
Only 12% of votes were in, with Collins leading Gideon 55%-39%.
The race is the costliest political race in Maine history, as the two candidates and their allies together spent more than $120 million on television advertising alone.
In-depth news coverage of the Greater Boston Area.
Collins is battling for a fifth term against a candidate who drew donations for all corners of the country. Democratic support quickly coalesced around Gideon as Collins' vote for Trump's Supreme Court nominee Brett Kavanaugh ensured the race would draw national attention and cash.
With the results expected to take time to tabulate, Collins spoke early on Tuesday night, only about a half an hour after the polls had closed.
"These are not easy times -- that's an understatement," she said. "A persistent, global pandemic continues to threaten the health of our people and the well-being of our economy."
Collins said she has always put the people of Maine first.
"You and you alone are my priority, and I have been honored to serve you each and every day," she said. "It's not about politics -- it's about Maine and Mainers."
Gideon's campaign manager released a statement early Wednesday thanking voters.
"It's clear this race will not be called tonight and we are prepared to see it through to the finish," campaign manager Amy Mesner said. "Over the coming days, we will make sure that every Mainer has their voice heard in this election."
The 2020 election in Maine marked the first use of ranked choice voting in a presidential contest in the U.S.
Maine voters first approved ranked voting in federal races in a statewide referendum in 2016. The Legislature later enacted a law to ensure that it's used in the presidential race.
Ranked voting is sometimes called an "instant runoff.'' But there's nothing instant about Maine's implementation of the voting system. If additional tabulations are required, then all the ballots from hundreds of municipalities have to be shipped to Augusta and entered into a computer which completes the additional tabulations.
The voting system is not used for state legislative or governor's races because of concerns it runs afoul of the Maine Constitution.
Other Maine races include:
There are five candidates on the presidential ballot, including Republican President Donald Trump and Democratic former Vice President Joe Biden. If none of them wins a majority of first-round votes, then there will be additional tabulations in which last-place candidates are eliminated and those supporters' second-place choices are reallocated to the remaining field.
As of Tuesday night, the race was still too close to call, with 49% for Trump and 48% for Biden with 13% of precincts reporting.
Democratic U.S. Rep. Jared Golden is battling Trump ally Dale Crafts in the vast, rural 2nd Congressional District. Golden led Crafts 52% to 47% with 20% of votes tallied on Tuesday night.
Golden, who narrowly defeated GOP Rep. Bruce Poliquin thanks to ranked voting in 2018, describes himself as a moderate voice for all Mainers. He has pledged to keep supporting small business and traditional rural industries, and to make access to health care a priority.
Crafts, a Republican, is a businessman and former state lawmaker who was counting on Trump's popularity in the 2nd Congressional District and endorsement carrying him to victory.
Democratic U.S. Rep. Chellie Pingree is considered a safe bet in her reelection battle against Republican Jay Allen. She led Allen 57% to 43% with 10% of precincts reporting on Tuesday night.
Pingree, 65, is seeking a seventh term in a liberal district that has been friendly to her over the years. If reelected, she would be the first person in six decades to be elected to more than six consecutive terms representing the 1st Congressional District.
Allen is a family physician and former Army doctor from the Bristol area who is running on a staunchly conservative platform.
A referendum on a proposed power corridor in western Maine wasn't on the ballot.
Opponents of Central Maine Power's $1 billion New England Clean Energy Connect that aims to serve as a conduit for Canadian hydropower obtained enough signatures for a statewide referendum. But the Maine Supreme Judicial Court ruled the referendum violated the Maine Constitution because referendums can be used only to nullify legislative actions, not state agency actions.