Kenyans vote Tuesday in general elections headlined by a too-close-to-call battle between incumbent Uhuru Kenyatta and his rival Raila Odinga, sparking fears of violence in east Africa's richest economy.
Tensions soared in the last days of the campaign with the murder of a top election official and opposition claims that one of its vote tallying centres was raided by police, heightening a feverish atmosphere of conspiracy and suspicion.
Odinga, 72, flagbearer of the NASA coalition, is taking his fourth and likely final stab at the presidency.
Right up until the eve of the vote, he insisted that Kenyatta's Jubilee Party planned to rig the presidential election, although he also congratulated his "worthy opponent" on his campaign.
In a bid to ease tensions Kenyatta addressed the nation Monday night, urging citizens to turn out to vote in great numbers, but to "do so in peace".
The polls are seen as a litmus test of Kenya's progress since a disputed 2007 election sparked two months of violence which left more than 1,100 dead and 600,000 displaced.
Kenyans will vote in six different elections, choosing governors, lawmakers, senators, county officials and women's representatives in local races also rife with tension.
However all eyes are on what is set to be the last showdown of a dynastic rivalry that has lasted more than half a century since the presidential candidates' fathers Jomo Kenyatta and Jaramogi Odinga went from allies in the struggle for independence to bitter rivals.
The men belong to two of the country'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.
Justus Nyang'aya, of Amnesty International's Kenya section, wrote in the Daily Nation that because of this "elections here are a do-or-die affair. It is as if the election of one of their own transforms the life of every member of the community. We all know that does not happen."
Forecasters say the vote is too close to call, however a run-off is unlikely.
Both candidates are so certain of victory that Nic Cheeseman, professor of African politics at Birmingham University in England, warns they may have "talked themselves into a corner."
"It seems almost inevitable that whoever loses will question the result. The question is not whether or not they will accept the result but what they will do when they don't accept it," he told AFP.
There are more than 19 million registered voters in the nation of 48 million. Half are aged under 35.
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.
However he is also criticised for soaring food prices -- with prices jumping 20 percent year-on-year in May -- and massive corruption scandals on his watch.
More than 150,000 security forces -- including wildlife, prison and forestry officers -- have been deployed for the vote from at 6am (0300 GMT) to 5pm (1400 GMT).
There are some 10,000 accredited observers, according to the electoral commission.
Former US president Barack Obama, whose father was born in Kenya, called on the eve of the vote for a peaceful election.
"I urge Kenyan leaders to reject violence and incitement; respect the will of the people," Obama said in a statement.
Analysts agree that the most critical aspect to the election's success is whether a biometric system of voter identification and tallying works on the day.
This system was introduced after the marred 2007 election -- which Odinga said he lost due to rigging. However in 2013 elections electronic glitches forced polling officials to resort to manual counting.
The tension around the electronic system increased after the poll commission's top IT manager Chris Msando was found strangled and tortured in a forest outside Nairobi.
The commission said its system had not been compromised by the murder, and a dry run of the tallying process went off without a hitch this week.
Nevertheless, many have stockpiled provisions or left cities for their ethnic heartlands both to vote and out of fear for their safety.