A group of former lawmakers and mayors quit the main opposition Democratic Party on Monday, saying they would join a new party that former DP leader Lee Nak-yon is trying to launch, amid attention over how deep the DP's split will go.

The departures of the five people -- former lawmakers Shin Kyoung-min and Choi Woon-youl, former Goyang Mayor Choi Sung, former Bucheon Mayor Jang Deog-cheon and former Jecheon Mayor Lee Keun-kyu -- came four days after Lee Nak-yon left the DP to create a new party of his own ahead of April's general elections.

A day before Lee's departure, three incumbent lawmakers -- Reps. Cho Eung-chon, Kim Jong-min and Lee Won-wook -- also left the DP, criticizing the way DP Chairman Lee Jae-myung runs the party, amid views that they are unlikely to win party nominations in the upcoming elections.

The series of departures raised questions about whether there will be more people leaving the DP, especially sitting lawmakers, and how much impact these will have on the parliamentary elections less than three months away.

On the side of the ruling People Power Party, former PPP leader Lee Jun-seok left the party in late December and is making preparations to launch a new party amid speculation that defectors from both sides could join hands to create a "big tent" party.

Also Monday, Rep. Ryu Ho-jeon of the minor opposition Justice Party also quit the party.

But the DP's leadership is skeptical of the possibility that more lawmakers could leave the party.

"Some incumbent lawmakers who expect to lose the party nominations could leave the party, but they won't have much of an impact," a DP official said.

Lee, whose envisioned party is accepting promoters until midnight, anticipated that more people would join.

"More than 20,000 have signed up as of Sunday night. This is more than 100-fold of the 200 required by the Political Parties Act," Lee said in a radio interview Monday, projecting the number to rise later in the day.

When asked about how many seats his party aims to win in the upcoming elections, Lee said it would be "at least 50 to 60."