The results of the runoff elections will determine which party controls the U.S. Senate -- and voters are nearly split on their preference, preliminary exit poll results show.

Forty-nine percent prefer Republican Party control, while 48% prefer control by the Democrats, based on the preliminary results.

The GOP needs either seat to retain control of the Senate, while the Democrats need both to win control.

Voters also were nearly split in their vote for president in the general election, based on the preliminary results -- suggesting that Democrats were holding their own in runoff turnout.

Voters in the race between Democrat Raphael Warnock and Republican Kelly Loeffler report having voted a dead-even 47%-47% Donald Trump-Joe Biden, preliminary results show. In the contest between Democrat Jon Ossoff and Republican David Perdue, it’s about the same -- 48%-47% Trump-Biden, based on preliminary results.

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

Polls across the state are closing as a flurry of advocates urge those who haven't voted and are still standing in line to stay past 7 p.m. and make sure their ballots are cast.

Georgia voters also had until 7 p.m. to return absentee ballots in drop boxes across the state.

A few polling precincts have gotten judicial extensions to be open past 7 p.m.: one in Gwinnett County, two in Columbia County, one in Tift County and two in Chatham County. There was also an accident near a polling place in Ware County that may lead to a judicial order extending poll closing time, said Gabriel Sterling, the state voting system implementation manager.

Sterling, in the most recent election update, described the day overall as "smooth voting, steady voting."

He said the state was getting reports of longer lines forming in Houston, Cherokee, Paulding and Forsyth counties with wait times approaching an hour, but not going over.

-ABC News' Quinn Scanlan

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

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