Outgoing President Uhuru Kenyatta, having served the constitutionally limited two terms, is backing one-time foe Raila Odinga, 77, to succeed him.
His decision followed a falling out with Deputy President William Ruto, 55, who had expected to be endorsed.
More than 22 million Kenyans have registered to vote.
The results of the last presidential election in 2017 were annulled after the Supreme Court ruled that the electoral commission had not followed the law when it came to the electronic transmission of the vote tallies from the polling stations.
Judges ruled that “illegalities and irregularities” had taken place.
A re-run was won by Mr. Kenyatta, but boycotted by Mr. Odinga – the main opposition candidate at the time.
The chairman of the electoral commission, Wafula Chebukati, who was also in charge of the 2017 vote, has frequently tried to reassure Kenyans that his team will be up to the task this time.
But Monday’s logistical problems have increased the pressure on him.
Baba v Hustler
This election looks like it will be a tight race between frontrunners Mr. Odinga and Mr. Ruto.
Two other candidates – David Mwaure and George Wajackoya – are also in the race.
Despite the campaign being dominated by issues, ethnic loyalty may also play a part in determining how people vote.
For the first time in the multi-party era, none of the main candidates are from the country’s largest ethnic group – Kikuyu.
But knowing that those votes are vital, both have chosen Kikuyu running mates.
To win the presidential race in the first round, a candidate needs:
- more than half of all the votes cast across the country
- at least 25% of the votes are cast in a minimum of 24 counties.
Voters will also be choosing MPs and senators to go to the national parliament, county governors, and county assembly members, as well as 47 women’s representatives, to sit in the National Assembly.
On election day, voters will have their fingerprints scanned to check their identity but a printed register can also be used if the machines fail.
Each voter will then be given color-coded ballot papers for each of the elections, which they will mark in a private booth and drop in the relevant ballot boxes.
Counting will start at the polling stations shortly after voting ends. Officials will then take a photo of the final tally and send the image to both the constituency and national tallying centers.
To ensure transparency the media, political parties, and civil society groups have been urged to run their own tallies using final results declared at the more than 40,000 polling stations.
However,Â afterÂ examiningÂ theÂ paperÂ andÂ digitalÂ ballotsÂ submittedÂ toÂ theÂ nationalÂ countingÂ center,Â onlyÂ theÂ electoralÂ commissionÂ canÂ proclaimÂ theÂ presidentialÂ election’sÂ victor.
TheÂ leadingÂ candidatesÂ forÂ presidentÂ haveÂ swornÂ toÂ respectÂ theÂ outcomeÂ ofÂ theÂ vote.