Conservative Yoon Suk-yeol won South Korea's presidential election Thursday, with the political novice and avowed anti-feminist immediately promising a more hawkish policy on the nuclear-armed North.

After a bitter, hard-fought election campaign, Yoon, formerly a top prosecutor who has never held elected office, was declared winner as rival Lee Jae-myung from the incumbent Democratic Party conceded defeat.

The victory of his People Power Party looks set to usher in a more muscular foreign policy for the world's 10th-largest economy after the dovish approach pursued by outgoing President Moon Jae-in during his five years in office.

Yoon will immediately have to confront an assertive Pyongyang, which has embarked on a record-breaking blitz of weapons tests this year, including a launch just days before the election. He vowed Thursday to "sternly deal" with the threat posed by Kim Jong Un's regime.

"But the door to dialogue is always open," he told supporters after visiting the national cemetery in Seoul.

Yoon has also called for a more robust relationship with ally Washington and spoke to U.S. President Joe Biden early Thursday, vowing to maintain "close coordination" on North Korea.

His victory margin was razor-thin: Yoon had 48.56% of the vote against Lee's 47.83%, according to South Korea's National Election Commission.

Despite a campaign dominated by mud-slinging, voter turnout was 77.1%, including record early voting, with interest strong and the stakes high in the country of some 52 million. "After a divided electorate has produced a divided government, Seoul may struggle to pursue policies of reform rather than politics of retribution," said Leif-Eric Easley, a professor of international studies at Ewha Woman's University in Seoul.

Moon's Democratic Party has a super-majority in the country's parliament, which could frustrate Yoon, who has no legislative experience, from pursuing his starkly different agenda. "His lack of experience on any real policy making is a serious concern," Karl Friedhoff of the Chicago Council on Global Affairs told Agence France-Press (AFP).

Yoon's election is a dramatic redemption for South Korea's conservatives, who were left in disarray in 2017 after their president Park Geun-hye was impeached.

It could restart the "cycle of revenge" in South Korea's famously adversarial politics, analysts say, where presidents serve just a single term of five years and every former living leader has been jailed for corruption after leaving office.

Yoon threatened to investigate outgoing President Moon Jae-in on the campaign trail, citing unspecified "irregularities."

But in his victory speech, he struck a more conciliatory tone, telling the country: "The competition is over now, and everyone must make joint efforts to become one." The frontrunners, who were both so unpopular that local media branded it the "election of the unfavorable," were neck and neck in the polls for months.

Yoon clinched victory because voters wanted a "change of power," not because they strongly supported him or his agenda, analyst Park Sang-byoung told AFP.

"Moon enjoys high approval ratings, but it couldn't measure up the people's demand for change," he said.

With such razor-thin support, it will be risky for Yoon to pursue the outgoing administration legally after he assumes office, Park added.

'My heart is very heavy'

Young swing voters were a decisive factor in the race, analysts said, with top concerns being skyrocketing house prices, social inequality and youth unemployment.

He also specifically courted disgruntled young male voters with a promise to abolish the gender equality ministry because South Korean women do not suffer from "systemic gender discrimination," despite evidence to the contrary.

"My heart is very heavy and desperate," said Kim Ju-hee, a women's rights activist.

Yoon's win has "set a precedent where a president-elect can openly ridicule women," she added.

Exit polls showed Yoon getting 58.7% support from men in their 20s than Lee at 36.3%. But for women in their 20s, Lee received 58% to Yoon's 33.8%.

"The widespread support Yoon enjoys from young men is, frankly, absolutely terrifying from a woman's point of view," academic and female voter Keung Yoon Bae told AFP. Voters wore medical masks to cast their ballots, as an omicron spike sent cases skyrocketing and forced over a million people to self-isolate at home. The country amended its electoral laws to allow them to vote and people also embraced early voting in record numbers.

Yoon will formally succeed Moon in May. Despite not achieving a promised peace deal with North Korea, the incumbent remains popular.