Seoul; South Korea's conservative ruling party may have lost its parliamentary majority in Wednesday's general election, exit polls by three TV channels showed.
The polls said the Saenuri Party was forecast to win between 118 and 147 seats in the 300-member National Assembly.
The main opposition Minjoo Party was expected to secure between 97 and 128 and the splinter opposition People's Party to win between 31 and 43 seats.
"Obviously, we're worried about the exit poll results but we will calmly wait until the final ballot counting results are returned", Saenuri's parliamentary floor leader Won Yoo-Chul said on national KBS TV.
The elections were clouded by North Korean nuclear threats and the multiple challenges facing Asia's fourth-largest economy, as President Park Geun-Hye enters the final stretch of her term in office.
Political power in South Korea is firmly concentrated in the presidency and elections to the single-chamber national assembly are traditionally dominated by local issues.
It is expected to become clear at about 1500GMT if Saenuri has lost its majority.
Observers, however, cautioned that exit polls have been wrong in the past five parliamentary elections.
If the ruling party, which won 152 parliamentary seats four years ago, fails to hold a majority it would be forced to rely on independent lawmakers to retain power in parliament.
Rising unemployment, plunging exports and worryingly high levels of household debt have led to criticisms of Park's handling of the economy and, by extension, of her ruling conservative Saenuri Party.
Dissatisfaction is especially high among young people, with the jobless rate among those aged 15-29 at record levels.
The left-wing opposition has sought to frame the vote as a referendum on Park's economic policies, but has suffered from factional infighting and breakaways that threaten to split the liberal vote to Saenuri's advantage.
Kate Kim, an unemployed 25-year-old college graduate, said that crippling levels of joblessness had persuaded her and many of her previously apathetic friends to vote.
"This is the first time I have voted... Our country desperately needs change, especially for young and jobless people like me," Kim said.
All 300 seats in the legislature are up for grabs, with 253 chosen in first-past-the-post constituency elections, and the remaining 47 elected on a separate ballot via proportional representation.
Analysts had predicted Saenuri's chances would receive a boost from surging military tensions on the divided peninsula.
But the exit polls indicated that threats from North Korea may have failed to aid of the ruling party, traditionally regarded as hawkish on security issues.