Prime Minister Lee Nak-yon is the front-runner to become Moon's successor in various opinion polls, while the next presidential race is more than two years away.

Lee is reportedly hoping to return to the ruling Democratic Party (DP) to play a role in the April 15 general elections in 2020.

Lee, a former South Jeolla Province governor, is said to be seeking to join a contest himself as well to become a lawmaker again. If he wins in a hotly contested constituency, he would be able to further solidify his foothold in the liberal party.

Lee has already become the longest-serving prime minister in South Korea since it introduced the current direct presidential election system in 1987. He took office weeks after Moon's inauguration in May 2017.

For months, there has been talk that Moon will likely carry out a major Cabinet reshuffle affecting the prime minister before the end of this year.

Local media have churned out reports of possible candidates to replace him.

Until early this week, Kim Jin-pyo, a four-term DP lawmaker, was reported to be the favorite. Some said he could be a good choice at a time when South Korea's economy is confronted with deepening woes, having worked as finance minister and deputy minister for economy for two years beginning in 2003.

He's also known for relatively good relationships with many politicians, not just with the ruling bloc but also the opposition one.

But civic groups, which advocate liberal policies, have openly argued that he's not suitable for the post. They claim Kim was against several economic reform measures, including opposing the raising of corporate taxes and calling for a delay in imposing taxes on religious figures.

Kim eventually asked the president to withdraw him from consideration, according to news reports.

Instead, another ruling party heavyweight, Rep. Chung Sye-kyun, has emerged as a strong candidate.

Conservative newspapers take issue with his career as National Assembly speaker from 2016-2018, saying it's inappropriate to nominate him for the top administrative position given the principle of the separation of powers.

Also on a media-reported shortlist of candidates are Won Hye-young, a five-term lawmaker of the DP who announced that he would not run in the 2020 general elections, and Chin Young, minister of the interior and safety.

Some observers are not ruling out the possibility that Moon will keep Lee in the job to avoid political controversies in the National Assembly's confirmation hearing process.

What's more urgent is to appoint his justice minister pick, Choo Mi-ae, who has yet to go through a confirmation hearing. The National Assembly is also embroiled in a do-or-die fight over the handling of electoral and prosecution reform bills.

"I don't think there will be any announcement in connection with the (next) prime minister today or tomorrow, at least," a Cheong Wa Dae official said, suggesting Moon is not rushing over the matter.

He doesn't have much time, however, if he wants to have a new prime minister. A public servant seeking to run in the April 15 elections should resign no later than 90 days ahead of the date, which falls on Jan. 15, under relevant legislation.

Many expect Moon to make a decision before heading to China on Dec. 23 for an annual group summit with the leaders of China and Japan. (Yonhap)