Three members of the main opposition Democratic Party either have or will declare presidential bids soon.
Two-term Chungcheongnam-do Governor Ahn Hee-jung announced his candidacy in Seoul on Sunday, vowing fresh, young leadership.
Seongnam Mayor Lee Jae-myung made his announcement on Monday, vowing fundamental changes.
He promised to lead the push for a more fair economy.
Seoul Mayor Park Won-soon is planning to formally announce his bid early next month.
On the other side of the political spectrum
Former Supreme Council member Rhee In-je is the first member of the ruling Saenuri Party to throw his hat into the ring, and has vowed to reform the nation's conglomerates to create a fairer society.
Former Saenuri floor leader Won Yoo-chul is also planning to declare his bid early next month.
There are also two candidates from the newly-formed Righteous Party, which broke away from Saenuri last month.
Nam Kyung-pil, the current Gyeonggi-do Province governor, and Yoo Seong-min, a former Saenuri floor leader, are scheduled to make their announcements on Wednesday and Thursday.
Both are seen as advocating for a strong market economy, but with a greater emphasis on welfare than their Saenuri Party counterparts.
Another minor party candidate declared her candidacy last week.
Justice Party leader Sim Sang-jeung pledged to create a welfare state and reduce the nation's working hours to the level of the OECD average.
Missing from this list are three other major candidates who are expected to declare soon --
former main opposition party leader and one-time presidential candidate Moon Jae-in, former UN Secretary-General Ban Ki-moon and former minor opposition People's Party leader Ahn Cheol-soo.
They are reportedly still mulling over the timing and location of their announcements.
"The latest polling shows that Moon Jae-in is still in the lead, with nearly 30 percent support."
In fact, Moon has a 10-point lead over Ban, according to the survey conducted by Realmeter and Maeil Business on over 25-hundred adults last week.
Filling out the survey's top five were Lee Jae-myung, Ahn Cheol-soo and Ahn Hee-jung, in that order.
Park Ji-won, Arirang News.