Lee Suk-joon (R), a former minister for government policy coordination, submits former Prosecutor General Yoon Seok-youl's application to register as a preliminary presidential candidate to the National Election Commission in Gwacheon, south of Seoul, on Monday. (Yonhap)

Registration for preliminary presidential candidates opened Monday, kicking off what appears to be one of the most crowded presidential races in the nation's history.

The National Election Commission (NEC) began the seven-month early registration period for candidates hoping to run in the March 9 election to pick a successor to President Moon Jae-in, whose term ends on May 9.

Registrants are allowed to conduct limited campaign activities ahead of an official registration set for mid-February.

More than a dozen figures have announced their intention to run, led by Gyeonggi Province Gov. Lee Jae-myung and former Prosecutor General Yoon Seok-youl.

Yoon was the first to submit his candidate application early Monday at the NEC office in Gwacheon, south of Seoul.

After submitting his application, Yoon issued a statement pledging to make "a country with the people where justice and common sense stand tall."

The ruling Democratic Party (DP) on Sunday narrowed down its primary contenders to six, including Gov. Lee, former party chief Lee Nak-yon, former Prime Minister Chung Sye-kyun and former Justice Minister Choo Mi-ae.

The liberal party plans to pick its candidate in September.

In the main opposition People Power Party (PPP), four prominent members, including former Prime Minister Hwang Kyo-ahn, have thrown their hats into the ring, and three others, including former presidential candidates Hong Joon-pyo and Yoo Seong-min, plan to declare their candidacy soon.

Yoo was the first among PPP contenders to submit his registration.

"I will become a president capable of solving the problems of our times by becoming the unified single candidate of the opposition bloc," Yoo said on social media after submitting his registration.

He also stressed the importance of the upcoming presidential race, arguing that it will "determine whether South Korea moves forward in a path of success or collapse on the threshold of becoming an advanced country."

Former Prosecutor General Yoon, the front-runner among the pack of conservative hopefuls, is pondering whether to join the PPP or launch his own party.

Observers also expect two other former members of the Moon administration -- former Board of Audit and Inspection (BAI) Chairman Choe Jae-hyeong and former Finance Minister Kim Dong-yeon -- to enter the conservative party, seeking its ticket to run for president.

Choe told reporters that he has yet to decide on a date to register for his candidacy, explaining that he had to handle the funeral of his father after deciding to join politics not too long ago.

The former BAI chief also said he plans to deliberate further on whether to join the PPP in his future political endeavor.

The PPP launched its primary committee Friday and plans to pick its flag-bearer in November.

Early registered candidates can open an election office, hire about 10 paid staff members and launch a fundraising organization.

They are allowed to conduct campaigns through phone calls, text messages and emails and distribute name cards and books of election pledges. (Yonhap)