With nearly all of Wednesday's votes tallied, the opposition Democratic Party (DP) and its satellite party were on course to win 176 of the country's 300 National Assembly seats.
The outcome, if confirmed, will leave Yoon as a lame duck for the three remaining years of his term in office.
Yoon's People Power Party (PPP), however, looked set to hang on to enough seats to prevent an opposition-led super-majority, which could have opened the door for the president's impeachment.
The DP won 161 seats that were directly up for grabs, Yonhap said, and was along with its partner projected to secure 16 more after accounting for seats decided on a proportional basis.
The PPP won just 90 seats directly, and was reportedly headed to capture 109 seats along with its satellite party.
Also in play was the new Rebuilding Korea party, led by former justice minister Cho Kuk, which capitalised on discontent with the two main parties to pick up a projected 12-14 seats.
"The figures today show the strong anger of people at Yoon for his two-year governance," political analyst Yum Seung-yul told AFP as exit polls came in Wednesday.
"What if he won't change even with this stunning election outcome? I think there will be even more public anger and that worries me."
- Lee's revenge -
Yoon beat Lee in South Korea's closest-ever presidential election in 2022 and has taken a tough line with the nuclear-armed North while improving ties with Washington and former colonial occupier Japan.
But Lee, while fending off a slew of graft probes he says are politically motivated, has secured revenge with the election result following a bruising and polarising campaign.
From the start of his presidency, Yoon has been unpopular, with ratings hitting the low 30s, and the PPP's lack of control of the National Assembly stymying his socially conservative legislative agenda.
This includes planned healthcare reforms -- that are backed by voters but have sparked a crippling strike by doctors -- and a pledge to abolish the ministry of gender equality.
PPP leader Han Dong-hoon had earlier said that "exit polls are disappointing... We will watch the vote count", the Yonhap reported.
- No babies -
On Yoon's side were shifting demographics, with voters aged 60 and older now outnumbering those in both their 20s and 30s in a country with the world's lowest birth rate.
Younger Koreans have been put off politics by a political class dominated by older men who ignore their concerns.
Many say this was underlined by the horrific 2022 Halloween crowd crush in Seoul that killed more than 150 mostly young people.
The younger generation is also struggling economically, with cut-throat competition in education, fewer job opportunities and sky-high housing costs.
"There is definitely less interest in this election among the people around me than last time. I think it is because they feel rather disappointed," business owner Kim Yong-ho, 24, said outside a polling station in Seoul's Gwangjin district.
The tone of the campaigning has also put many voters off, lacking in substantive policy debate and marked instead by shrill calls to "imprison" Lee or "punish" Yoon.
"I am truly ashamed of our country's politics and government," Kim Do-kyung, 47, an activist for migrant women and their children, told AFP.
This has been accompanied by hate speech and disinformation online that experts worry could lead to more attacks like the one on Lee in January and another weeks later.
- Onions -
The DP favours a less hawkish approach towards Pyongyang, and Lee has made a number of pro-China remarks. One doctored video showed him bowing to a statue of Mao Zedong.
It has also latched onto a gaffe by Yoon last month about the "reasonable" cost of green onions, a staple in Korean cooking that has soared in price.
The humble vegetable became a popular prop at DP rallies, and the election commission even banned voters from bringing them to polling stations.
burs-stu/ceb/cwl/nro/des
Related Links
Democracy in the 21st century at TerraDaily.com
| Subscribe Free To Our Daily Newsletters |
| Subscribe Free To Our Daily Newsletters |
