Moon Jae-in makes a speech at an event to declare their fair contest in the party's presidential primary in Seoul, South Korea, March 14, 2017. [Photo/Agencies]

SEOUL - The latest opinion poll in South Korea heralded a neck-and-neck race in the upcoming presidential election between Moon Jae-in of the biggest Minjoo Party and Ahn Cheol-soo of its splinter People's Party.

According to the survey released Wednesday, Moon kept the top post by gaining 38.0 percent support, followed by Ahn who garnered 34.4 percent support.

It was the first opinion survey after five major political parties ended primaries and fielded respective presidential candidates earlier this week.

The result was based on a survey of 1,042 voters conducted Tuesday. It has 3.1 percentage points in margin of error.

Moon, the runner-up to former President Park Geun-hye in the 2012 presidential election, was fielded as a single candidate in the opposition bloc four years ago thanks to Ahn.

At the time, Ahn abandoned his run for presidency to throw support behind Moon.

The software tycoon-turned-politician was respected especially in 2012 by younger generations as he developed and offered the country's first computer security program to private citizens free of charge.

Currently, Ahn seemed to be viewed as a center-right politician for his conservative stance on security issues and a liberal tendency on economic affairs.

Ahn, who had been affiliated with the Minjoo Party, defected from it and founded the People's Party in early 2016 together with tens of former Minjoo Party lawmakers.

Hong Joon-pyo of the former ruling Liberty Korea Party ranked third with an approval rating of 10.4 percent.

Sim Sang-jung of the progressive Justice Party came next with 3.6 percent, trailed by Yoo Seong-min of the Righteous Party, a conservative party breaking away from the Liberty Korea Party, with 2.1 percent in support scores.

On the assumption that the Liberty Korea Party and the Righteous Party agree to field Yoo as a single candidate, the poll showed Ahn's approval scores at 41.0 percent, higher than Moon's 39.0 percent.

The agreement on the single candidate in the conservative camp would encourage many conservative voters to move to Ahn.

If the two conservative parties and the People's Party agree to field Ahn as a single candidate, Ahn was estimated to win the upcoming election with 43.7 percent of ballots, beating Moon garnering 39.4 percent.

In a simulated two-way showdown between Moon and Ahn, the poll logged Ahn's approval scores at 47.0 percent while Moon's scores were 40.8 percent.

The overall survey results showed a strong anti-Moon sentiment among conservative voters, which was believed to be formed by local media reports.

Moon, the center-left politician and former chief of staff to late progressive President Roh Moon-hyun, has been exposed to and criticized by conservative local media outlets for a long time.

An early presidential election in South Korea is scheduled for May 9. The official three-week election campaign is set to kick off on April 17.