From first-time voters to those bent with age, from urbanites to ethnic Samburu warriors draped in colourful beads and carrying spears, thousands descended upon polling stations long before dawn to cast their ballots.
"I really hope for a change of leadership, I really hope for a change in the way we do politics. I want corruption out of the country", said Mary Wangu, 42, at a Nairobi polling station.
Electoral commission (IEBC) chief Wafula Chebukati said "voting was going smoothly" despite minor delays, technical hiccups and heavy rain slowing the process at some of the 41,000 polling stations.
All eyes are on the biometric voter identification and tallying system which suffered severe glitches in 2013 polls. The system is seen as crucial to a smooth election amid opposition accusations of a plot to rig the vote.
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Kenyans are no strangers to violent polls, and tensions have soared over fraud claims and the murder of an official in charge of the electronic voting system in the final days of campaigning.
The IEBC moved quickly to deal with complaints Tuesday, removing clerks in a polling station where ballot papers were pre-marked as "rejected".
In the port city of Mombasa a clerk was arrested for issuing double ballot papers to certan voters, local police said.
"I voted Raila, because he will be so much better to us. But if he does not win, it's ok. It's a democracy after all. Really, there's no need for violence," said Tom Mboya, 43, who works in construction and voted in the capital's largest slum Kibera.
The men belong to two of Kenya's main ethnic groups, Kenyatta from the Kikuyu, the largest, and Odinga from the Luo.
Both have secured formidable alliances with other influential communities in a country where voting takes place largely along tribal lines.
Odinga, 72, the flagbearer for the National Super Alliance (NASA) coalition, is taking his fourth and likely final stab at the presidency. He claims elections in 2007 and 2013 were stolen from him.
"To my competitors, in the event that they lose they should be able to accept the will of the people. I also want to say that if I lose, I will accept the will of the people," said Kenyatta.
Kenyatta, 55, is seeking re-election after a first term in which he oversaw a massive infrastructure drive and steady economic growth of more than five percent.
"Kenyatta has done a tremendous job, he has improved communications, built roads and other infrastructure, he has to keep the job," said Sashikat Bhaga, 68, in the Nairobi suburb of Parklands, home to many Kenyans of Indian or Pakistani origin.