Until 1900 hrs, 56.7 percent or some 3,770,000 of 6,652,106 registered voters went to the polls, the Centre for Free Elections and Democracy (CESID) said at a news conference.
CESID director Zoran Lucic said he expected the final turnout to be 60.3%.
Marko Blagojevic of CESID said that several dozen irregularities had been reported at 8,383 polling stations, but that the general impression was that the elections were in line with relevant standards.
CESID will announce the first estimates of election results around 2200 hrs, and the national election commission is expected to declare the final, official results until Thursday, January 25.