Notably, Moon received the highest approval ratings in all regions except for Gangwon Province and the southern resort island of Jeju.

It marks a rare occasion for a progressive candidate to stand as the No. 1 contender in North Gyeongsang Province and Daegu, where voters used to be strongly supportive of former President Park Geun-hye, who was recently removed from her office by the Constitutional Court.

Moon posted an approval rating of 36.6 percent in North and South Jeolla Province, regions that heavily lean toward the opposition bloc.

Even though Moon lost against Park in a 51.6 percent to 48 percent vote in the 2012 presidential race, the former party head then raked in 92 percent of the vote in Gwangju, the key city of the provinces.

Acting President and Prime Minister Hwang Kyo-ahn became the second-most favored candidate in North Gyeongsang Province and Daegu, but his overall rate fell 2.1 points to 9.1 percent, indicating a large number of voters were disappointed by Park's corruption.

South Korea must hold the presidential election in the next 57 days, following the ouster of Park. Most expect it to be held in early May, seven months earlier than presidential elections are typically held here.

The survey was conducted on 2,046 South Koreans with a margin of error of plus or minus 2.2 percentage points. (Yonhap)