People are voting in Kenya's general election amid fears that the result could trigger communal violence.
On the eve of the vote, President Uhuru Kenyatta appealed for calm in a televised speech.
He urged the 19 million registered voters to turn out in great numbers, but to "do so in peace". Queues formed early outside many polling stations.
The contest pits Mr Kenyatta against his long-time rival, Raila Odinga, and is seen as too close to call.
Mr Kenyatta, the 55-year-old son of Kenya's founding president, is seeking a second and final term in office.
The final week of campaigning has been marred by the murder of a top election official and claims of vote-rigging.
Observers say the leading candidates both avoided inflammatory speeches as polling day drew closer. In 2007 more than 1,100 Kenyans died and 600,000 were displaced after a disputed election - an outcome neither side wants to see repeated.
"After you cast your ballot, please go home," Mr Kenyatta said on Monday.
"Go back to your neighbour. Regardless of where he or she comes from, their tribe, their colour or their religion. Shake their hand, share a meal and tell them 'let us wait for the results,' for Kenya will be here long after this general election."
Opposition leader Mr Odinga, of the National Super Alliance, also addressed the public on Monday. He raised fears about vote-rigging and claimed the deployment of at least 150,000 members of the security forces was a ploy to intimidate voters.
However, he congratulated Mr Kenyatta on his campaign, describing him as a "worthy opponent".
"May the stronger candidate win tomorrow," he said.
Eight presidential candidates are on the ballot on Tuesday, with polls open until 17:00 local time (14:00 GMT).