SEOUL, April 16 (Xinhua) -- South Korean President Moon Jae-in's ruling Democratic Party won a landslide victory in parliamentary elections held amid the COVID-19 pandemic that delayed elections in other nations.

Preliminary results from the National Election Commission showed on Thursday that the Democratic Party secured 163 directly-contested constituency seats, while its sister Platform Party gained 17 proportional representations (PR) slots.

The quadrennial elections for the 300 members of the National Assembly were held nationwide on Wednesday to let voters cast ballots for 253 constituency seats and 47 PR slots.

It marked the first time since the constitution was amended in 1987 to end the past military dictatorship and adopt democratic elections that a single political party won three-fifths of the total parliamentary seats.

The main conservative opposition United Future Party and its satellite party garnered 84 constituency seats and 19 PR seats.

The minor progressive Justice Party won one constituency seat and five PR slots, while the center-left Open Democratic Party and the centrist People's Party won three respective PR seats.

Five independent candidates obtained the remaining constituency seats in the parliamentary elections, widely seen as a mid-term referendum on the Moon government.

The elections were held at a time of the COVID-19 outbreak across the world that delayed elections in other countries such as Britain, France and Australia.

Preparations were made to protect voters from possible infection while casting ballots, by disinfecting voting stations and marking the standing line at intervals of at least 1 meter.

Voters were allowed to enter the voting booths only after wearing masks, checking body temperature, rubbing their hands with sanitizer and putting on disposable plastic gloves.