Former President Barack Obama tweeted to Georgia voters that while state polls close at 7 p.m., they should stay in line if they've arrived at their polling location in time.

"You have the right to vote, no matter how long it takes," Obama tweeted.

Some precincts in the state will be open past 7 p.m. due to court orders.

Obama joined a virtual rally for Democratic candidates Rev. Raphael Warnock and Jon Ossoff earlier this month and has appeared in digital ads for both candidates. On Monday, the former president tweeted "the stakes could not be higher" in promoting the runoff elections.

A majority of voters in Georgia's Senate runoffs think the presidential election was fair, preliminary exit poll results show.

More than half -- 56% -- of voters think the presidential election in Georgia was conducted fairly, while 41% do not, according to the preliminary results.

President-elect Joe Biden defeated President Donald Trump by nearly 12,000 votes in Georgia. Trump repeatedly has made unsubstantiated claims of voter fraud in Georgia, among other states.

Most voters also express at least some confidence in the current runoff elections. Seventy-three percent are very or somewhat confident that votes in the runoffs will be counted accurately, while 26% are not very or not at all confident, according to the preliminary results. This is down from a similar question in November, when 85% were very or somewhat confident that votes in their state would be counted accurately.

-ABC News' Gary Langer, Christine Filer and Steven Sparks

Gabriel Sterling, the voting system implementation manager in Georgia Secretary of State Brad Raffensperger's office, provided an update on the runoff elections, reporting no major issues at this point in the day.

"The biggest thing is we have to deal with is rumors," Sterling said. "Everybody's kind of on edge for some of these things. But in general, it's been steady as she goes."

Sterling said that while there are also reports circulating about turnout, it's impossible for the state to know how many have voted so far Tuesday because the voting systems are not connected to the internet.

"So it's anecdotal evidence that we receive," he said. "If there's not lines, it doesn't mean that there's not a high turnout. It just means they're processing people."

Sterling predicted Tuesday's turnout could be as low as 600,000 or as high as 1.1 million, stressing, "We just have no way of knowing."

The maximum number of absentee ballots outstanding, he said, is 306,855. Sterling later tweeted a correction to the maximum number of potential outstanding absentee ballots, saying the correct number is 229,357. These are due by 7 p.m. when most polls close across the state.

Sterling said the public will know about the biggest bulk of votes Tuesday night, but it's unclear when final results will be known.

"We're gonna start getting results tonight. We're gonna get the biggest bulk of them, like we did last time, it depends on the margin," he said. "If I'm a betting person, which I'm not, I would say it's gonna be a couple of days, because I anticipate it will be a close race one way or the other."

-ABC News' Quinn Scanlan

Turnout among partisan groups is central to the outcome of the two runoff races in Georgia. In addition to Black and other racial and ethnic minority voters, another group to watch is evangelical white Christians, core Republicans.

Black voters appeared to hold on to their share of the state's electorate, according to preliminary exit poll results.

Black people -- a core Democratic group -- account for 29% of voters in these preliminary results, compared with 28% in November.

Evangelical white Christians account for 34% of runoff voters preliminarily, about the same as in November.

In purely partisan terms, Republicans outnumber Democrats by three points in these preliminary results, 39% to 36%.

-ABC News' Gary Langer, Christine Filer and Steven Sparks

President-elect Joe Biden said that he feels "optimistic" about Tuesday's pivotal runoff elections in Georgia during an interview on V103 with Kenny Burns, a local Atlanta radio host.

"I'm doing really well, feeling really optimistic about today," Biden told Burns.

Asked what specific policies he expects to come before the Senate this year that make it so critical for Democrats Jon Ossoff and Rev. Raphael Warnock to win, Biden cited both the need to get $2,000 payments to struggling Americans and harshly criticized the federal government’s vaccine distribution plan at length, saying Congress needs to be able to provide support to get the vaccine out to all Americans.

"Right now, for example in Georgia, you have only about 75,000 people who have gotten the vaccination, yet you got about a half a million doses of that vaccine in the state. There's no planning. The federal government has done virtually no planning. It's one thing to get a vaccination -- to get to get the actual vial -- sent to you in a frozen pack. It's another thing to get it into a needle and the vaccination into somebody’s arm," Biden said.

"So I'm gonna need [Congress'] help in making sure that we establish thousands of federally-run and federally-supported community vaccination centers of various sizes across the country. Located in high school gyms or NFL football stadiums," Biden said, adding that the vaccination project has to involve multiple levels of the government including FEMA and the under his administration vaccines will be free.

"The inability of the president and the Republican leadership, and Trump in particular, preventing that from being made available to the states is just -- it's just almost criminal in my view. And people are dying,” Biden later added.

The president-elect once again hammered Georgia’s two Republican senators and candidates, Kelly Loeffler and David Perdue, saying they’ve forgotten who they have been elected to represent.

"Look here's the thing that's happening. Because of the Republican senators of Georgia, their loyalty is to Trump, not to the people of Georgia. I mean, when I got sworn into the Senate I didn't swear allegiance to the president, whether it was a Democrat or Republican. I'm not going to have any senators swear allegiance to me. It's to the Constitution and to the state of Georgia, that's who you represent," Biden said.

-ABC News' John Verhovek, Beatrice Peterson and Molly Nagle