Voter turnout for Wednesday's by-elections was running slightly higher than previous races held during summer vacation season, reaching 21.8 percent as of 2 p.m., the national election watchdog said.
The by-elections cover eight National Assembly seats, which have been left vacant from resignations or court convictions of as many lawmakers over the past year.
The National Election Commission (NEC) said some 297,000 voters out 13.6 million people in the eight constituencies cast their ballots starting from when polls opened at 6 a.m.
The 1 p.m. figure is 8.6 percentage points higher than the last by-elections held in July, in 2006. The turnout for last year's by-elections
in October was 22.1 percent at 1 p.m.
The NEC predicted Wednesday's turnout would reach near 30 percent.
During the 2005-2009 period, the average turnout in by-elections was 32.4 percent, while two midsummer by-elections in 2006 and 2008 recorded only 24.8 percent and 23.3 percent, respectively.
The 30 percent mark is considered a breaking point, with lower turnout usually giving the ruling party an edge, but a higher figure favoring the opposition. A higher turnout often means more younger and left-leaning people have cast their votes.
The ballot will close at 8 p.m. and preliminary results are expected before midnight.