Nigeria’s main opposition parties have called for the country’s presidential election to be scrapped, alleging that results showing the ruling party’s candidate in the lead had been manipulated.

Early results have put Bola Tinubu from the ruling All Progressives Congress (APC) well ahead of the main opposition Peoples Democratic party (PDP) candidate, Atiku Abubakar, and the outsider third challenger, the Labour party’s Peter Obi.

But the count has been hit by multiple technical and logistical problems that the Independent Nigerian Election Commission (Inec) appears unable to resolve. It was expected to restart announcing results at 11am (10am Irish time) on Tuesday, but postponed this twice.

“The election is irretrievably compromised and we have totally lost faith in the entire process,” the Labour party chairman Julius Abure told reporters at a press conference alongside PDP representatives. “We demand that this sham of an election should be immediately cancelled ... We also call for a fresh election to be carried out,” Mr Abure said.

Electoral officials rejected the criticism.

“Contrary to the insinuation by both parties, results emanating from the states point to a free, fair and credible process,” Inec said in response. “It is only fair for aggrieved parties to allow the conclusion of the process and approach the courts with their evidences to pursue their cases.”

The election is the most competitive in Nigeria since the end of military rule in 1999.

Mr Tinubu (70), and Mr Abubakar (76), are seen as traditional politicians representing Nigeria’s established political elite. Mr Obi (62) is considered a reformist who has reached across the country’s faultlines to woo voters from all communities and ran a slick social media campaign to attract the young.

A Reuters tally of preliminary results early on Tuesday morning showed Mr Tinubu leading on about 36 per cent, with Mr Abubakar close behind with 30 per cent and Mr Obi on 20 per cent or about 3.8 million votes.

Another running total of officially declared presidential votes, compiled by local consultancy Stears, showed Mr Tinubu on 44 per cent, with Mr Abubakar on about 30 per cent and Mr Obi on 17 per cent on Tuesday at about 4pm local time. If provisional votes yet to be officially declared by Inec were included, Mr Obi would be in second place, six points behind the leader.

Senior officials close to Mr Tinubu have told the Guardian they are confident of victory and see “no pathway” for Mr Obi to take power.

Some results continue to surprise, however, such as Mr Obi’s victory in Lagos, Nigeria’s largest city and commercial powerhouse. Officials announced on Tuesday that Mr Obi had also won in Abuja, the capital.

[ Sally Hayden: Nigeria election background ]

Though the contest is still relatively close, Nigerian electoral law makes a runoff unlikely as the winning candidate needs only a plurality of votes, provided they get 25 per cent of the vote in at least two-thirds of the 36 states.

Experts warn that the problems with the count could lead to protracted contestation and even violence.

“Politics is very much like a business in the minds of many actors. It’s not about serving the people, it is about serving the self. So you see a very vociferous campaign and a great difficulty to accept defeat,” said Prof Abiodun Adeniyi, an expert in politics and communication at Baze University, Abuja.

On Monday night, Olusegun Obasanjo, the former president, warned of a “looming danger ahead” caused by the failure of systems that would electronically send results to a central computer.

The results were “not a true reflection of the will of Nigerians who have made their individual choice”, he said.

Election officials said the results had been fully authenticated and government loyalists accused the opposition of fomenting “lawlessness and anarchy”.

International observers have also criticised Saturday’s vote, which was largely peaceful despite expectations of widespread chaos and violence.

A team of observers led by Joyce Banda, the former president of Malawi, said delays on voting day, which led to many polling stations opening hours late, meant the election “fell well short of Nigerian citizens’ reasonable expectations”.

A European Union mission said the failures “reduced trust in the process and challenged the right to vote”.

Nigeria is contending with multiple intersecting crises including economic turmoil, extremism and criminality affecting much of the country. In recent weeks, an effort to replace almost all Nigeria’s banknotes – in part to reduce the widespread practice of vote-buying – has caused massive economic disruption and much popular anger.

However, analysts point out that seven elections have been held in succession and some Nigerian democratic institutions are growing stronger. That none of the main candidates are former military officers – a first for a Nigerian poll – is also viewed as an achievement.

There have been concerns raised about the limited number of women contesting the poll.

Evin Incir, the head of delegation of the European Parliament, said: “I wish to express my concern that less than 10 per cent of candidates were women. The next government and parliament should heed to the manifestos of the main political parties of Nigeria, which call for affirmative action, such as quotas.”