Kenya's opposition leader Raila Odinga appeared to be widening his lead in the country's presidential elections, with Saturday's provisional results giving him 3.7 million votes against his challenger, President Mwai Kibaki, in close pursuit with 3.4 million votes.

The Electoral Commission of Kenya (ECK) Chairman Samuel Kivuitu announced the provisional results from 159 constituencies, with almost two thirds of the votes cast in the Thursday presidential poll.

"This state of affairs is not satisfactory," Kivuitu told a news conference attended by party leaders, diplomats, journalists and foreign election observers as the main opposition complained the delay might affect the final vote outcome.

Kivuitu, trusted for his efficient management of the elections in 2002 and the 2005 referendum on a draft constitution for Kenya, said his attempts to get electoral clerks to file the results of the presidential elections had been futile.

"When we ring these places, we find the telephones are switched off. I am sure those delaying the results do not know what it means to be a fugitive. It is not a very nice word," he added.

The electoral body was preparing to declare the full results within hours, after most of the results from the 51 electoral zones, which had not been tallied, started streaming in.

"We are puzzled," Kivuitu said after announcing the provisional results.

President Kibaki is facing one of his toughest political contests in nearly half a century.

The incumbent, who entered politics in 1960, won the presidential polls in 2002 without much of a challenge, but has faced the tightest race for the presidency so far.

Kenya's 'five-in-eight constitutional rule' requires a presidential candidate to win the majority vote in addition to at least 25 per cent of the votes cast in five of the eight provinces to be declared winner.

Both Kibaki and Odinga have qualified.

Meanwhile, the opposition has urged President Kibaki to concede defeat.

The Orange Democratic Movement (ODM) has swept most of the parliamentary seats, gaining over 100 seats in the 210 member parliament.

The vote tallying in the 51 constituencies where results had not been received are on course to beating a Saturday deadline to have the full presidential results announced.

"If we don't receive the results quickly, we might announce these results. We are using all means, including the police, to monitor the activities in the areas where results have not been received," Kivuitu said.

Some 14.2 million Kenyans were eligible to vote in this year's general elections, but the results released so far showed a total tally of 7.5 million votes.