The joint exit poll by KBS, MBC, SBS predicted that Park, the daughter of late former President Park Chung-hee, would win a majority, defeating Moon, the standard bearer of the main opposition Democratic United Party (DUP), who is expected to secure 48.9 percent of the vote.
The 1.2 percentage point edge by the 60-year-old candidate Park, however, is within the 1.6 percentage point margin of error in the poll conducted on 86,000 people nationwide.
A separate exit poll by cable broadcaster JTBC also predicted a narrow win for Park, estimating that she would secure 49.6 percent against Moon's 49.4 percent.
But another cable broadcaster YTN's exit poll produced a different result, forecasting that Moon would win by obtaining 49.7 percent to 53.5 percent, with Park securing 46.1 percent to 49.9 percent.
With 17.6 percent of the votes counted as of 8:22 p.m., Park won 52.7 percent of the total votes cast against 46.8 percent for Moon. Due to the conflicting exit polls, the winner is unlikely to be confirmed until midnight.
Expectations are rising at the Saenuri Party but party officials said they will watch the vote count to the end, guarding against any hasty optimism.
"This is going to be a very close race and we will have to wait and see," said party chairman Hwang Woo-yea.
The DUP, on the other hand, said there is no need to jump to conclusions because Park's lead is very small and could be overturned as the vote counting continues.
Party officials said the exit polls did not reflect last-minute voters and absentee and overseas votes.
"In the end, (Moon) will emerge victorious," a DUP lawmaker claimed.
Preliminary voter turnout in Wednesday's presidential election, meanwhile, was estimated at 75.8 percent as of 6 p.m,, up sharply from the previous presidential polls in 2007 when the tally reached just 63 percent. The high turnout reflects the high interest South Koreans have in the close race, according to the state election watchdog.
About 30.7 million out of a total of 40.5 million eligible voters have cast their ballots since voting began at 6 a.m. at 13,542 polling stations nationwide, the National Election Commission (NEC) said.
The polls closed at 6 p.m.