The liberal Democratic Party on Wednesday began a 10-day vote to pick its candidate for the upcoming presidential election.

The polling of the non-party electorate began at 7 a.m. at 250 stations across the country. The results will be combined with the outcomes of upcoming telephone surveys and additional polls by party members and representatives, the party said.

The outcome of Wednesday's vote will not be immediately made available. 

Currently, four contenders are seeking to become the standard-bearer of Korea's largest party in the May 9 presidential election.

They are Moon Jae-in, former party chief and frontrunner in most recent polls on the upcoming election, South Chungcheong Province Gov. An Hee-jung, Seongnam City Mayor Lee Jae-myung and Goyang City Mayor Choi Sung.

The party's primary vote involves some 2.14 million non-party members who registered as the electorate. They will participate either in Wednesday's vote or telephone surveys, party officials said.

"Those who opted to cast ballots directly at polling stations will vote today, while the rest will be given a call later for phone surveys," an official said.

The party will also hold a vote among its party members in five different areas including Seoul from Saturday.

The party plans to pick its nominee after a final vote in Seoul on April 3.

Should no candidate secure a majority of the vote, a runoff election will be held and the party candidate will be named on April 8.

Korea's presidential election has traditionally been held in December but it has been moved up to May following the Constitutional Court ruling earlier this month that upheld a parliamentary impeachment of former President Park Geun-hye due to a corruption scandal.

The Constitution requires an election to be held within 60 days of the removal of a president. (Yonhap)