Deputy President William Ruto led a tight presidential race against opposition leader Raila Odinga, official results reported by media showed on Monday, with an announcement from electoral authorities due at 1200 GMT.

Slow progress by the electoral commission in tallying Tuesday's vote have fed anxiety in East Africa's most economically advanced country, which has a recent history of violence following disputed elections.

In its latest announcement on Saturday of officially verified results with a little more than a quarter of votes counted, the commission put Odinga in the lead with 54% and Ruto on 45%. Subsequent tallies by Kenyan media groups and Reuters, however, put Ruto at 51-52% and Odinga at 48%.

The tallying centre where the announcement will be made was packed with party officials who were entertained by musicians calling for calm.

Purity Njeru, the electoral commission's head of communications, said the declaration of the presidential winner would be made at 1200 GMT.

The winning candidate must get 50% of votes plus one.

President Uhuru Kenyatta, who has served his two-term limit, fell out with Ruto after the last election and this time endorsed Odinga for president.

Ruto heads the Kenya Kwanza (Kenya First) Alliance and served as a lawmaker and minister for agriculture before becoming deputy president.

Odinga is running for president under the Azimio La Umoja (Declaration of Unity) Alliance, which includes Kenyatta's Jubilee party. He is a former cabinet minister and prime minister.

CHECKS AND BALANCES

Media reported more than three quarters of votes counted.

In official verified results reported by the independent and privately owned Nation Media Group, with 253 constituencies counted out of a total of 291, Ruto had 51% of the vote and Odinga 48%.

The Standard Group - likewise independent and privately owned - reported Ruto ahead, again with 51% of the vote against Odinga's 48% and also with 253 constituencies tallied.

A Reuters tally of 268 preliminary constituency-level results at 1100 GMT on Monday showed Ruto on 52% and Odinga at 48%. Two minor candidates shared less than a percent between them.

Reuters did not include 20 forms in the count because they lacked signatures and totals, were illegible or had other problems.

The preliminary tally was based on forms that were subject to revision if any discrepancies were discovered during the official verification process.

The many checks and balances were designed to try to prevent the kind of allegations of rigging that provoked violence after the 2007 vote, when more than 1,200 people were killed.

In 2017, after the Supreme Court quashed the result over irregularities in the electoral process, more than 100 were killed.

Crispinus Kokonya in Eldoret, a region where Ruto has his largest support base, said the outcome was still unclear.

"So we are now waiting upon Chebukati... what he says we will follow," he said referring to the electoral commission Chairman Wafula Chebukati.

Others said the wait was damaging business.

"We are losing money - it's causing a lot of anxiety and anger," said Alphonce Otieno Odhiambo a farmer and a motor bike taxi driver in Kisumu, an Odinga stronghold.