South Korea's two main parties are locked in a close race for control of parliament that is seen as a preview of presidential elections later this year.

Exit polls from Wednesday's voting left analysts unable to predict whether President Lee Myung-bak's ruling New Frontier party will hold onto its majority in parliament. Official results were not expected until after midnight (1500 UTC).

Han Myung-sook, leader of the opposition Democratic United Party, said while voting earlier Wednesday that she was very nervous about the result.

“From the start we did our best to be the ruling party, but at the moment we are very nervous and we will be very anxious until we see the result of the vote count.”

Prime Minister Kim Hwang-sik also spoke to reporters while voting, urging citizens to exercise their democratic rights.

“I hope that all South Korean citizens exercise their right to vote after careful consideration in order to provide a strong foundation for the further development of the nation.”

The voting was to fill 300 seats in the National Assembly, with 246 of the legislators to be elected directly. The remainder are chosen through proportional representation.

The results will have an impact on the December presidential vote. This is the first time in 20 years that the parliamentary and presidential elections are taking place in the same year.

The opposition has accused the party of supporting the rich and privileged at the expense of ordinary South Koreans.

Elections for South Korea's unicameral parliament are held every four years. The country has about 40 million eligible voters.