Kenya’s Supreme Court has declared President Uhuru Kenyatta's election win invalid due to irregularities committed by the election board and has ordered a new election within 60 days.

The decision to cancel the result, the first of its kind in Kenya's history, sets up a new race for the presidency between Mr Kenyatta and veteran opposition leader Raila Odinga.

Opposition leader Raila Odinga

East Africa's biggest economy has a history of disputed elections. A row over the 2007 poll, which Mr Odinga challenged after being declared loser, was followed by weeks of ethnic bloodshed in which more than 1,200 were killed.

"The declaration (of Mr Kenyatta's win) is invalid, null and void," said Judge David Maranga, announcing the verdict backed by four out of the six judges and drawing cheers outside the court from Odinga supporters.

"The first respondent (the election board) failed, neglected or refused to conduct the presidential election in a manner consistent with the dictates of the constitution," the judge said.

International observers had said they saw no sign of manipulation of voting and tallying at polling stations.

Several observers said the opposition did not conduct a parallel tally and had not challenged results with complete data of their own.

Many voters in the west of Kenya, Mr Odinga's stronghold, and along the coast, where there is traditionally large support for the opposition, feel neglected by the central government and shut out of power.

"This indeed is a very historic day for the people of Kenya," Mr Odinga said after the decision.

"For the first time in history of African democratisation a ruling has been made by a court nullifying irregular elections for the president."

Mr Kenyatta has said he disagreed with the ruling, but added that he would respect the decision and urged citizens to do the same.

In a televised address he said: "The court has made its decision. We respect it. We don’t agree with it. And again, I say peace ... peace, peace, peace. That is the nature of democracy".

Mr Odinga has contested the last three elections and lost each time. After each one, he has claimed the votes were marred by rigging. In 2013, the Supreme Court dismissed his petition.

This time, his team focused on proving that the process for tallying and transmitting results was flawed, rather than proving how much of the vote was rigged.

Residents in the western city of Kisumu, where Mr Odinga has strong backing, celebrated in the streets. Motorcycle drivers hooted their horns.

"Today is a special today and I will celebrate until I am worn out", said one man.

Kenya's dollar bonds fell after the ruling.

Meanwhile, Kenya's electoral commission has vowed to make staff changes ahead of the new presidential vote.

Independent Electoral and Boundaries Commission chairman Wafula Chebukati took note of the Supreme Court ruling on last month’s presidential election.

Speaking at a press conference he said: "The commission intends to make internal changes to our personnel ... as we prepare for the fresh presidential election in 60 days."

He ruled out resigning himself, saying he had not been implicated in any wrongdoing.

"The commission invited the office of the director of public prosecutions to urgently investigate and prosecute any of our staff that may have been involved in violations of the election offenses act," he said.