Lee Jae-myung, the presidential nominee of the ruling Democratic Party (DP), registered with the national election watchdog as a preliminary presidential candidate on Tuesday.

Lee's aides, DP Reps. Park Hong-keun and Park Chan-dae, filed the registration on the candidate's behalf at the National Election Commission's office in Gwacheon, 18 kilometers south of Seoul.

The move came the same day Lee stepped down as governor of Gyeonggi Province to focus on his presidential campaign.

"I begin a new first day," he wrote on Facebook. "I am both excited and fearful as I leave behind my usual path to work and set out to meet the people as a preliminary presidential candidate."

Lee pledged again to fulfill his calling despite the heavy responsibility he feels and vowed to create a better future for the nation.

The nominee met with President Moon Jae-in at Cheong Wa Dae Tuesday in a key step to beginning his campaign in earnest for the presidential election slated for March 9. (Yonhap)