Polls opened across Kenya at 0600 local time (0300 GMT) after a vigorous and occasionally violent campaign.
More than 14 million people are expected to cast their votes at about 27,000 polling stations for a president and 210 parliamentarians.
Turnout is reportedly high. This man jumped out of a classroom window in Nairobi, as the doorway to the polling station was blocked with waiting voters.
Pollsters say it is one of Kenya's most closely contested elections, with President Mwai Kibaki facing his toughest challenge from his former ally, Raila Odinga.
Many lined up before dawn. In Kisumu, in Nyanza Province, most night clubs and pubs remained closed on Wednesday night so voters would be sober ahead of polling.
Violence broke out in the region on Tuesday, with at least three policemen killed after Mr Odinga's supporters accused them of planning to rig elections.
In Mr Odinga's constituency in Kibera slum in the capital, Nairobi, there was chaos as people tried to force their way into a classroom to vote after being left off the voters' roll.
In Kibera, voting was delayed for several hours as some ballot boxes were missing lids.
Mr Odinga, whose name was missed off the voters' roll, was eventually able to vote...
There have been worries about violence after Mr Kibaki and Mr Odinga's supporters clashed in the capital on Christmas Eve, the last day of campaigning.
Mr Kibaki told his cheering supporters that he was confident he would be given a second term in office.