SEOUL, May 10 (Xinhua) -- Liberal Moon Jae-in has won a landslide victory in a South Korean presidential by-election amid growing hopes for a new society following the impeachment of his predecessor over corruption scandal.

Moon of the biggest Minjoo Party gained a 41.1-percent support, defeating his two main rivals by a large margin, according to the final results released by the national election commission on Wednesday.

It can be seen as a sweeping victory given the five-way presidential race.

The country's incoming president celebrated with jubilant supporters gathering at the Gwanghwamun square in central Seoul around midnight as Moon's victory was assured by local media outlets in an early stage of vote count.

In the televised speech, Moon told supporters that he would become a president for all the people from Wednesday, and he would become a president of unity, caring about those who did not support him in the election.

This election was "a great victory of great people," said Moon who pledged to become a proud president of the Republic of Korea (ROK) that is great, righteous and confident. The ROK is an official name of South Korea.

Before the speech, he told reporters at his party's building that he would achieve the two main goals of reform and unity as people had wished for.

Reform and national unity will be high on the agenda under the Moon administration.

People demand reform on conglomerates, called chaebol here, prosecutors governed by the presidential power and inequalities of income and wealth, which are seen by many as the most urgent issue that should be tackled immediately.

"Overwhelming is public demand for the transfer of power regardless of whoever represents the Minjoo Party as two conservative governments messed up our country in the past 10 years," said Seo Bok Kyung, a researcher at Sogang University's Institute of Political Studies.

Jang Seok-joon, vice president of local think tank Future Politics Center, said the demand for the transfer of power led to strong support for Moon, thanks to the downfall of conservatives.

Four other major candidates made concessions to Moon, even before less than 10 percent of votes were counted. The concessions led local media outlets to predict an assured election of Moon.

Hong Joon-pyo of the conservative Liberty Korea Party, with which ousted President Park Geun-hye was affiliated, garnered a higher-than-expected electoral score of 24.0 percent.

Hong said in a televised address that he would accept the election result and be satisfied with restoring his party.

Ahn Cheol-soo of the centrist People's Party suffered a heavy defeat with 21.4 percent support as his scores once came closer to Moon's in opinion polls released in early April.

Ahn told the televised speech that he would humbly accept the election result, hoping that his country could go toward the future with a new president.

Yoo Seong-min of the minor conservative Righteous Party said that he had a telephone conservation with Moon to congratulate his victory, asking Moon to humbly hear the voice of voters who did not support him.

Sim Sang-jung of the minor progressive Justice Party gave a phone call to Moon, offering her heartfelt congratulations to him and saying Moon bore a heavy burden as a president facing tremendous assignments.

Yoo and Sim gained 6.8 percent and 6.2 percent each in support scores.

Moon, the elected president, will have no transition period as it is the first by-election caused by the removal of Park from office over corruption allegations.

Moon is widely forecast to appoint part of the presidential staff later Wednesday, while naming the prime minster in the near future.

The cabinet can be formed when the prime minister suggests ministers to Moon who will confirm the proposals. The prime minister is required to be subject to the parliamentary hearing.

The final turnout was 77.2 percent, or 32,808,377 voters among the electorate of 42,479,710 people. It was higher than the previous election's 75.8 percent in 2012.