Ruling party presidential candidate Lee Jae-myung is leading his main opposition rival Yoon Suk-yeol by 37 percent public support to 31 percent, a survey showed Friday.

Lee's support rose 1 percentage point from last week, while Yoon's rose 5 points, according to the Gallup Korea survey conducted on 1,001 adults from Tuesday to Thursday.

In third place was Ahn Cheol-soo, the presidential candidate of the minor opposition People's Party, at a record high 17 percent, up 2 percentage points from last week, followed by Sim Sang-jeung of the minor progressive Justice Party at 3 percent.

In the hypothetical scenario of Yoon and Ahn merging candidacies, Yoon of the People Power Party led Lee of the Democratic Party 42 percent to 40 percent.

With Ahn as the unified candidate, Ahn beat Lee 45 percent to 38 percent, according to the survey.

By age group, Lee garnered over 40 percent among voters in their 40s and 50s, while Yoon earned over 40 percent among those older than 60.

Among voters in their 20s, the three leading candidates were neck and neck at 24 percent for Ahn, 23 percent for Yoon and 22 percent for Lee.

The proportion of undecided voters dropped to 10 percent overall as Ahn's popularity grew among young voters, the pollster said.

President Moon Jae-in's approval rating stood at 42 percent, up 1 percentage point from last week, while his disapproval rating also rose 3 points to 53 percent.

The survey had a margin of error of plus or minus 3.1 percentage points at a 95 percent confidence level. (Yonhap)