South Koreans voted Wednesday in by-elections seen as a test for parties and potential candidates before parliamentary and presidential polls next year. Morning turnout was higher than in last year\'s parliamentary by-elections, a trend generally considered favourable to opposition parties, but observers avoided making predictions in the tightly contested races. Three parliamentary seats, one provincial governorship and local posts are up for grabs. Polls will close at 8pm (1100 GMT Wednesday) and results are expected around midnight. The outcome cannot affect the overwhelming parliamentary majority held by the conservative Grand National Party (GNP) of President Lee Myung-Bak. But a poor showing by either the ruling or opposition party could prompt a party leadership change and affect the prospects of presidential hopefuls. South Korean presidents serve a single five-year term, meaning Lee himself cannot stand again in the December 2012 election. A general election will be held in April 2012. Wednesday\'s polls became a higher-stakes game when Sohn Hak-Kyu, a presidential aspirant and head of the left-leaning opposition Democratic Party, decided to run in a southern suburb of Seoul. Polls suggest a neck-and-neck race between Sohn and former GNP leader Kang Jae-Sup in the Bundang B parliamentary constituency, a traditional conservative stronghold. A victory for Sohn would boost his presidential ambitions but a defeat could deal a serious blow. At Gimhae near the southeast coast, candidate Lee Bong-Soo from an opposition coalition faced off against the GNP\'s Kim Tae-Ho. Kim has tried to restore his tarnished image after quitting his bid for the prime minister\'s post last year over ethical questions. Gimhae is the home town of former left-leaning President Roh Moo-Hyun, who committed suicide in 2009 when his family became the subject of a graft probe. A victory for Kim in a district where Roh is fondly remembered would fuel a political comeback. The GNP is also seeking the governorship of Gangwon province but is not contesting a third parliamentary seat seen as a liberal stronghold.