The ruling party in South Korea has lost its majority in parliament after elections aimed at boosting its position, exit polls suggest.

Exit polls forecast the Saenuri party to retain a slight lead over opponents but not enough to secure a majority in the 300-member National Assembly.

Saenuri previously had only a slim majority in the assembly.

It meant that President Park Geun-hye's time in office had been hampered by legislative gridlock.

She was hoping a stronger showing of support in the National Assembly would help her to push through labour and economic reforms before her term in office expires in about 20 months' time.

Park has been criticised over her handling of the economy, which has seen rising unemployment - particularly among the young - falling exports and high levels of household debt.

Polls ahead of the election suggested Park's centre-right party was on course to secure a substantial majority of seats.

But as the votes started coming in, South Korea's public broadcaster KBS predicted that Saenuri would win between 121-143 seats while the main opposition Minju Party would secure between 101-123 seats.

Other TV exit polls suggested a similar outcome.

"Obviously we're worried about the exit poll results but we will calmly wait until the final ballot counting results are returned," Saenuri's Won Yoo-chul told KBS TV. The final results are expected to become clear by 1500 GMT, AFP news agency reports.

Voters cast ballots at nearly 14,000 polling stations to elect 253 of the 300 lawmakers. The remaining 47 proportional representation seats are allocated to parties according to the numbers of votes they receive overall.