The ruling party's better-than-expected performance in Wednesday's local elections was seen as a blow to the main opposition party even though no clear winner emerged from the polls.

The ruling Saenuri Party and the main opposition New Politics Alliance for Democracy (NPAD) were set to each win at least seven of the 17 metropolitan mayoral and gubernatorial seats up for grabs, with the remaining three races too close to call until early Thursday morning, according to the National Election Commission (NEC).

As the first nationwide elections under President Park Geun-hye, the polls were seen as a crucial test of public support for the conservative administration that has drawn fire for its botched handling of the deadly sinking of the ferry Sewol in April.

Park took office in February 2013.

Of the seven seats certain to go to the ruling party, four were for the mayors of Daegu, Incheon, Busan and Ulsan, while the remaining three were for the governors of South and North Gyeongsang provinces and Jeju Province, the NEC said.

The ruling party expressed satisfaction with the outcome.

"I believe we put up a good defense even in the midst of the Sewol disaster," Yoon Sang-hyun, the ruling party's secretary general, said in a meeting with reporters. "Our determination and sincerity to build a new Republic of Korea came through."

NPAD, meanwhile, scored victories in the race for the crucial Seoul mayorship, its traditional strongholds of Gwangju and South and North Jeolla provinces, as well as Daejeon, Sejong and South Chungcheong Province.

Seoul Mayor Park Won-soon of NPAD beat Chung Mong-joon of the ruling party to win re-election.

Park thanked Seoul's citizens for their support, vowing to work together with all citizens including those who didn't vote for him.

"My election is the victory of all citizens who, in their grief over the Sewol, demanded fundamental change," he said in a press conference at his campaign office, referring to the ferry that sank off the country's southwest coast on April 16, leaving more than 300 people dead or missing.

"Dear citizens, I have chosen to part with things that are worn out. I will now walk toward a new era in silence," he added.

Chung, a seven-term lawmaker and former vice president of football's world governing body, FIFA, conceded defeat in a separate press conference at his own campaign office.

"(Park's) victory appears certain," he said. "I'm sorry for being unable to return the support of Seoul's citizens."

The Seoul mayorship carries extra weight in South Korean politics as it is often deemed a stepping stone to the presidency.

Former Seoul Mayor Lee Myung-bak was elected president in 2007, running on his accomplishments as the top administrator of the city.

Park has denied having presidential aspirations, but his re-election is widely expected to consolidate his status as a potential presidential contender.

The race was too close to call in the three remaining regions of Gangwon Province, Gyeonggi Province and North Chungcheong Province, with vote counting still underway as of early Thursday.

Opposition parties had called for judgment on the incumbent administration, saying the government failed to protect the lives of the public.

The ruling party, meanwhile, campaigned on a promise to fix the social abnormalities that were revealed through the ferry tragedy.

It also urged voters to protect the president in the face of growing attacks from the opposition party.

"The 'Park Geun-hye marketing' strategy had an effect, and the 'hidden votes' in the Saenuri Party's power bases appear to have demonstrated their might," Lee Taek-soo, the head of polling agency Realmeter, said in a phone interview with Yonhap News Agency. "On the other hand, NPAD failed to properly take advantage of the Sewol disaster."

Analysts had offered the view that the older and more conservative generations, who traditionally support the ruling party, would come out of their "covers" after having kept a low profile during the mourning period that followed the tragedy.The effect of the elections on the political landscape remains to be seen.

Some offered the view that the Park administration would regain confidence to push forward major policies. The president could also limit the scope of a planned government reshuffle to just the prime minister and several other Cabinet members, and retain her chief of staff, Kim Ki-choon, and other key presidential staff despite earlier calls for their dismissal.

South Korean presidents have often used government shakeups as a key political tool to overcome trouble and start anew as such reorganizations are taken as an acknowledgment of fault and an expression of commitment to work harder with a new lineup.

The elections for a total of 3,952 officials, including 17 metropolitan mayors and provincial governors and 226 heads of low-level administrative units, as well as local council members and education superintendents, were the first nationwide polls in 18 months.

Voter turnout in Wednesday's local elections reached a provisional 56.8 percent, according to a preliminary count by the election watchdog. The turnout was the highest for nationwide local elections since the first such polls in 1995 when it reached 68.4 percent. (Yonhap)