Rep. Kim Eun-hye of the main opposition People Power Party explains the temporary omission of turnout data from Siheung for the June 3 local elections at the National Assembly in Seoul, Tuesday. Yonhap

More than 3,600 votes were temporarily omitted from turnout data for the June 3 local elections in Siheung, the election watchdog acknowledged Tuesday, amid an investigation into alleged data manipulation by election officials.

According to election data obtained by Rep. Kim Eun-hye of the main opposition People Power Party, voter turnout in the city, just south of Seoul, stood at 22,914 at 9 a.m. on election day, before surging to 42,482 in the next hourly update at 10 a.m.

The National Election Commission (NEC) attributed the sudden surge to an error by the local election commission that failed to report 3,612 votes from three neighborhoods for the 9 a.m. update.

Instead of correcting the 9 a.m. turnout, the Gyeonggi Province election office, which oversees voting in the city, instructed for the votes to be included in the next update, resulting in distorted turnout data.