The main opposition People Power Party (PPP) kicked off the final week of its presidential primary Monday as the two front-runners appeared to be locked in a tight race for the nomination.

The party's standard-bearer is scheduled to be determined and announced at a national convention Friday after four days of polling party members and the general public on their most favored candidate.

The four candidates are former Prosecutor General Yoon Seok-youl, PPP Rep. Hong Joon-pyo, former Rep. Yoo Seong-min and former Jeju Gov. Won Hee-ryong.

Party members will be able to vote via smartphone on Monday and Tuesday and via automated phone calls on Wednesday and Thursday.

The general public will be asked to vote during phone interviews on Wednesday and Thursday.

The candidate who wins the most votes after combining the ballots of party members and the general public by a 50:50 ratio will take home the nomination. Friday's event will mark the end of the third and final round of the primary and there will be no run-off.

"To ensure the Republic of Korea doesn't leave you out as it prepares for the future, I ask all party members to take part in the mobile vote starting at 9 a.m. tomorrow," PPP Chairman Lee Jun-seok wrote on Facebook on Sunday. "If the turnout exceeds 70 percent, I will quit carbs for a month."

Political watchers say a key deciding factor in the outcome will be the votes of new party members who joined the PPP after the first national convention in June.

The number of members with voting rights has more than doubled from 280,000 to 570,000 in that period, and around half of the new members are young voters in their 20s to 40s, whereas most of the conservative party's members have so far been in their 50s or older.

Yoon and Hong, the front-runners in the race, have each claimed they will emerge as the winner because opinion surveys have shown Yoon to be more popular among party members and Hong to be leading among the general public.

In a survey by the Korea Society Opinion Institute, which asked respondents to pick the most competitive PPP candidate for the March 9 presidential election, Hong beat Yoon 38.6 percent to 34 percent, followed by Yoo with 11.4 percent and Won with 3.5 percent.

The survey was conducted Friday and Saturday on 1,016 adults nationwide and had a margin of error of plus or minus 3.1 percentage points at the 95 percent confidence level.

In a hypothetical two-way race with ruling Democratic Party presidential nominee Lee Jae-myung, the candidates were neck-and-neck with Yoon beating Lee 36.6 percent to 36.5 percent and Hong trailing Lee 34.2 percent to 35.2 percent, the survey showed. (Yonhap)