NAIROBI, Kenya -- Kenyan President Uhuru Kenyatta on Wednesday led challenger Raila Odinga by a significant margin in partial election results, but the opposition said the counting process was flawed and disputed the tally.

The website of Kenya's election commission showed Kenyatta with just over 55 per cent and opposition leader Odinga with nearly 44 per cent after votes were counted from more than two-thirds of the 40,833 polling stations. However, the commission did not release information about which constituencies had been counted, so it was unclear whether Kenyatta strongholds or opposition centres, or some combination, had yet to be tallied from Tuesday's vote.

That prompted sharp criticism from Odinga, who also ran against Kenyatta in the 2013 vote and unsuccessfully challenged the results in court with allegations of vote-tampering. The longtime opposition figure also ran in the 2007 vote, which was followed by violence fueled by ethnic divisions that killed more than 1,000 people.

"A clean credible process would by now have a dashboard showing all tallies from all constituencies to add to a sum total so that country can know which part of the country has been counted and what the votes are," Odinga said in a statement Wednesday.

"The system has failed," Odinga said. He added that the election commission "has just said that no parties have disputed the results. How do parties dispute results which they do not even know their origins?"

Election officials acknowledged the opposition objection, but defended their actions.

"We believe that by displaying results, we have been doing well to enhance transparency and accountability in the electoral process, consistent with the commitment the commission has made to the Kenya people," said commissioner Consalata Bucha Nkatha Maina, vice chairwoman of the election commission.

The commission's CEO, Ezra Chiloba, also said a results screen at the commission's counting centre had frozen because too much data was being received, and that tallies would be updated later Wednesday morning.

A similar situation with a systems failure in the 2013 election led to Odinga's legal challenge at the time, though Kenya's Supreme Court ruled in favour of Kenyatta by validating the results.

Kenyatta, the 55-year-old son of Kenya's first president after independence from British colonial rule, campaigned this year on a record of major infrastructure projects, many backed by China, and claimed strong economic growth. Odinga, 72, also the son of a leader of the independence struggle, cast himself as a champion of the poor and a harsh critic of endemic corruption.

However, many voters were expected to vote along ethnic lines. Kenyatta is widely seen as the candidate of the Kikuyu people, the country's largest ethnic group. Odinga is associated with the Luo voting bloc, which has never produced a head of state. There were six other presidential candidates, though they lack the wide support of the top two.

The winner of the presidential race must get more than 50 per cent of the votes as well as one-quarter or more votes in at least 24 of Kenya's 47 counties, according to officials. If the front-runner falls short of those benchmarks, the two top contenders will contest a run-off vote.

Former U.S. Secretary of State John Kerry, who is the chief election observer for The Carter Center, described Tuesday's vote as "an inspiring day in Kenya watching democracy in action."

"Enthusiastic voters not fazed by long lines," he tweeted.