Nairobi — Some 22.1 million registered voters are on Tuesday voting to elect the country's fifth president and successor to the incumbent Uhuru Kenyatta with long queues being registered in various polling stations from as early as 5.30am.

Many Kenyans were woken up by clarion calls from vuvuzelas for them to go vote in the hotly contested elections.

The process that kicked off at 6am will go on up to 5pm in 46,229 polling stations.

The electorate will also cast votes for governors, Members of Parliament and other Members of County Assembly positions.

"I reached here at 1.00am. I could not sleep as I have to vote for Raila Amollo Odinga to ensure he gets into State House. We expect a lot of things from him," one voter stated.

"We wanted to come and vote as early as possible and then go about a various business as we wait for the results."

Despite not being eligible for election after serving two terms as limited by the constitution, Kenyatta remains centre-stage after he declared his backing for Azimio La Umoja One Kenya Candidate Raila Odinga, who is running for the presidency for a record fifth term.

Deputy President William Ruto, who served two terms with Kenyatta but has since fallen out with his boss is vying on a United Democratic Alliance Ticket.

Another key issue to watch will be whether two less prominent contenders, George Wajackoyah and David Mwaure, can peel enough votes away from the two main candidates to force a run-off.

Although the campaign has been largely peaceful, its tone has sharpened in the final weeks, which has seen the two main candidates argue that winning is a matter of political and economic survival.