Voting time has been extended by one hour and polling stations will be closing at 11 p.m. instead of 10, the Electoral Commission said.
The decision was taken after queues built up in several localities, notably those where elections are also being held for local councils.
A spokesman for the commission said the extension applies to all polling stations. Anybody still in the queue at 11 p.m. will still be allowed to vote.
Voter turnout at 2 p.m. was 45 percent, four percent lower than at the 2003 general election, but voters appeared to have decided to vote late, with many polling stations reporting a build-up of voters, especially after Saturday Mass.