Seoul, South Korea: Left-leaning former human rights lawyer Moon Jae-In began his five-year term as president of South Korea Wednesday, following a landslide election win after a corruption scandal felled the country's last leader.  

Tuesday's ballot was called after Park Geun-Hye was ousted and indicted for corruption, and took place against a backdrop of high tensions with the nuclear-armed North.

Voters were galvanised by anger over the sprawling bribery and abuse-of-power controversy that brought down Park, which catalysed frustrations over jobs and slowing growth.

Moon, of the Democratic Party, who backs engagement with the North, promised unity after final results from the National Election Commission (NEC) showed he took 41.1 percent of the vote -- some 13.4 million ballots. 

Conservative Hong Joon-Pyo -- who dubbed Moon a "pro-Pyongyang leftist" was far behind on 24.03 percent, with centrist Ahn Cheol-Soo third on 21.4 percent. 

Voter turnout was at its highest in 20 years, the Yonhap news agency reported. Moon's inauguration ceremony was expected to take place at the National Assembly at midday (0300 GMT), the agency said, after the NEC confirmed the start of his mandate.

The result was "a great victory of great people" who wanted to create "a country of justice... where rules and common sense prevail", Moon told cheering supporters on Gwanghwamun Square in Seoul -- where vast crowds gathered for candlelit protests over several months to demand Park's removal.

The graft scandal plunged the country into political turmoil and bitter division, but Moon promised healing, telling the crowd: "I will be president for all South Koreans."

On the square among the crowd, Koh Eun-Byul, 28, told AFP: "I am so happy because now there is hope for some meaningful change."

Washington, which remains Seoul's most important ally and has a large security presence in the South, on Tuesday congratulated Moon on his landslide victory.

"We look forward to working with president-elect Moon to continue to strengthen the alliance between the United States and the Republic of Korea and to deepen the enduring friendship and partnership between our two countries," White House press secretary Sean Spicer said in a statement.

Tokyo, which has strained relations with its neighbour over issues including territory and Japan's wartime sex slavery, also congratulated Moon. 

Prime Minister Shinzo Abe said he looked forward to meeting the new leader, adding: "Japan and South Korea are facing common challenges in East Asia, led by responses to the North Korean issue.

"I believe the two countries can further contribute to peace and prosperity of the region by working together."

The campaign focused largely on the economy, with North Korea less prominent. But after a decade of conservative rule Moon's victory could mean significant change in Seoul's approach towards both Pyongyang and key ally Washington.

The 64-year-old -- accused by his critics of being soft on the North  -- advocates dialogue to ease tensions and to bring it to negotiations. He is seen as favouring more independence in relations with the US, Seoul's security guarantor with 28,500 troops in the country.

Their presence, he told reporters during the campaign, was "important not only to our own security but also to the global strategy of the US".

The North has carried out two nuclear tests and a series of missile launches since the start of last year in its quest to develop a missile capable of delivering a nuclear warhead to the US mainland.

Washington has said military action is an option, sending fears of conflict spiralling.

- Acute division -

South Korea's rapid growth from the 1970s to 1990s pulled a war-ravaged nation out of poverty but slowed as the economy matured, and unemployment among under-30s is now at a record 10 percent.

Frustration over widening inequality in wealth and opportunities fuelled anger over Park's scandal, which exposed the cosy and corrupt ties between regulators and powerful family-oriented conglomerates, known as chaebols, that have endured for decades.

Park is in custody awaiting trial over corruption for offering governmental favours to top businessmen -- including Samsung heir Lee Jae-Yong -- who allegedly bribed her secret confidante, Choi Soon-Sil.