Liberal politician Moon Jae-in has been declared the winner in South Korea's presidential election, ending nearly a decade of conservative rule.

"I will be president for all South Koreans," Moon, 64, told cheering supporters in the capital, Seoul, on Tuesday after his rivals conceded defeat.

"This is a great victory of great people who stayed with me to create a country of justice ... where rules and common sense prevail," the former human rights lawyer said.

The election body said Moon gathered 41 percent of the votes, comfortably edging conservative Hong Joon-pyo and centrist Ahn Cheol-soo, who gathered 24 percent and 21 percent of the votes, respectively.

Moon will immediately begin his single five-year term.

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According to Yonhap news agency, voter turnout was about 77 percent, the highest in a presidential election since 1997.

Al Jazeera's Craig Leeson, reporting from Seoul, said Moon's victory was a sign of growing frustration over the country's numerous domestic challenges, including corruption and record-high unemployment.

"Certainly, [this was] a protest vote, with the majority of voters signalling they want an end to the collusion between political parties and big business," Leeson said.

"They want reform of the economy; they want jobs and that is something that Moon promised very vigorously in his campaigning leading up to this election."

The result is expected to end months of political turmoil stemming from a parliamentary vote in December to impeach former president Park Geun-hye over an extensive corruption scandal.

The Constitutional Court upheld her impeachment in March, making her the country's first democratically elected leader to be removed from office and triggering a snap election to choose her successor.

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"People have wanted a cleaner, fairer and more equal government but the previous government has not been successful on that matter," Shin Se-don, a professor of economics at the Sookmyung Women's University, told Al Jazeera from Seoul.

"As a result, people came out to the streets last October in the so-called 'candlelight revolution', so this special election is a kind of culmination of the people's choice of a new government," he added.

But Shin predicted that Moon is going to have a "hard time" to deliver on some of his election promises as he does not enjoy a majority in parliament.

"I foresee enormous trouble for the president to handle the matters in the Congress."

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After being sworn in, Moon is likely to quickly name a prime minister, who will need parliamentary approval. The main cabinet posts, including about national security and finance, do not need legislative confirmation.

Moon favours dialogue with North Korea to ease tension over its accelerating nuclear and missile programme.

He advocates a two-track policy of seeking dialogue with the North while maintaining pressure and sanctions to encourage change.

He also wants to reform powerful family-run conglomerates, such as Samsung and Hyundai, and boost fiscal spending to create jobs.