Deputy President William Ruto has expressed confidence in winning the presidential election, moments after he cast his vote in his home town in the Rift Valley region.

"I look forward to a victorious day," he told journalists.

"I'm very confident that the people of Kenya will make choices that will take our country to the future... it's upon all of us to respect the choices of the people."

Mr Ruto, 55, is making his first attempt at the presidency after being a deputy president for 10 years.

His main challenger, Raila Odinga - a long-serving opposition leader - is running for president for a fifth time.

The police are urging Kenyans to leave polling stations after casting their votes and wait for the results at home so as to maintain order and peace.

“In today's poll, after you have made your decision known at the ballot, we ask that you support our security efforts by waiting for the poll results at the comfort of your homes,” the National Police Service says in a statement.

“We all want to live in an orderly society that respects the rule of law and one that is considerate to the wellbeing of its people,” it adds.

The police are providing security for the polling exercise across the country, with officers dedicated to each of the more than 46,000 polling stations.

During campaigns some politicians had urged supporters to remain at polling stations on voting day in order to "guard their votes".

Queues started building up at polling station in the capital, Nairobi, on Monday night.

The BBC's Anne Soy says one queue stretched well over 200m by early Tuesday. The people at the front said they arrived before 21:00 on Monday.

Margaret Mwangi, 59, a fruit hawker, decided not to go home for the night. She camped at the station waiting to vote.

She’s second in the queue and hopes to go home after voting to follow the news on television.

Image source, AFP/Reuters

There are four candidates vying for the top job:

• David Mwaure - Agano Party of Kenya - the trained lawyer and preacher announced a run for the presidency in 2013 but later shelved his ambition
• Raila Odinga - Azimio la Umoja coalition - the former prime minister and veteran politician is making his fifth attempt to become president
• William Ruto - United Democratic Alliance - this is the first run for the presidency for the current deputy president

• George Wajackoyah - Roots Party of Kenya - the lawyer and educationalist is making his first bid for the presidency

Voting has started across the country after polling stations opened at 06:00 local time.

Voters are choosing a new president as well as five other election races.

Deputy President William Ruto, one of the frontrunners for the presidency, has voted together with his wife at Kosachei Primary School in Kenya's Rift Valley region.

Martha Karua, the running mate of presidential candidate Raila Odinga, has also cast her ballot in Gichugu, Kirinyaga County, in central Kenya.

Polling stations will close at 17:00 local time (14:00 GMT) and anyone still in the queue at closing time will be allowed to cast their ballots.

Vote counting will begin soon after.

Across the country, Kenyans have woken up to go vote.

In the western city of Kisumu, BBC's Roncliffe Odit has shared pictures of long queues at polling stations even before the official polling time begins.

In the capital, Nairobi, queues have also been forming, as these pictures by BBC's Peter Njoroge show:

Voters have already started queueing up at polling stations across the country before voting starts at 06:00 local time (03:00 GMT).

A BBC reporter has been to one of the polling centres at a primary school in the capital, Nairobi.

"We are ready," an electoral commission official at Moi Avenue Primary School polling station tells him:

A few kilometres away in Westlands Primary School, hundreds of voters are already in the queue. Some say they got there at 03.00.

Election observers from the European Union and other organisations have arrived at the station.

Queues have formed at polling stations in other parts of the country.

Kenyans are electing a new president to succeed Uhuru Kenyatta, whose second and final five-year term draws to a close.

Voters are also due to choose MPs and governors, but these elections have been postponed in four areas due to errors on printed ballots.

Queues have been forming at the more than 46,000 polling stations across Kenya’s 290 constituencies ahead of the 06:00 local time (03:00 GMT) opening time.

They will remain open for 11 hours and anyone still in the queue at closing time will be allowed to cast their ballots.

Welcome to our special coverage of the Kenyan general election as millions vote for a new president, parliament and local governments.