Nigeria’s electoral commission has delayed the presidential election until 23 February, making the announcement just five hours before polls were set to open on Saturday.

It cited unspecified “challenges” amid reports that voting materials had not been delivered to all parts of the country.

“This was a difficult decision to take but necessary for successful delivery of the elections and the consolidation of our democracy,” commission chairman Mahmood Yakubu told reporters in the capital, Abuja, late on Friday night. He said more details would be released on Saturday afternoon.

President Muhammadu Buhari faces a tight election contest in Nigeria, Africa’s largest economy, top oil producer and most populous nation, against the main opposition candidate, businessman and former vice president Atiku Abubakar.

The election has been seen as a referendum on Buhari’s first term, which has been marred by his prolonged absence due to illness, a weak economy, and the government’s failure to effectively tackle corruption and insecurity.

But the 84 million people registered to vote across Nigeria are waking up to learn that they will not be able to take part in the poll for another week.

Nigerians have to return to their home states to cast their votes, and many of those who have travelled across the large west African country in order to do so will not be able to repeat the journey next weekend.

On Friday, planes leaving Abuja airport were full of people going home in order to take part in the election. On election day, travel is restricted, and most people walk to polling stations to cast their votes.

Elections for the state governors, due to be held on 2 March, were also delayed by a week. The cost of the election, already expected to be 242 billion naira ($670m) will increase now.

The country’s presidential elections in 2011 and 2015 were also delayed over logistics and security issues.

The decision to delay this year’s vote was criticised by the chairman of the main opposition People’s Democratic Party, Uche Secondus, said the move was an action that was “dangerous to our democracy and unacceptable”, adding that it was part of an attempt by Buhari to “cling on to power even when it’s obvious to him that Nigerians want him out”.

The president’s ruling All Progressives Congress party criticised the Independent National Electoral Commission (INEC) for the delay.

Buhari “cooperated fully with INEC by ensuring everything it demanded to conduct free and fair elections were promptly made available,” it said in a statement. “This news is therefore a huge disappointment to us.”

An electoral commission official said that “some result sheets and some ballot papers are reportedly missing. We want to track every (piece of) sensitive material, take inventory of what we have and what is missing”.

Breaking News: The #NigeriaDecides2019 Elections now to hold on; 23rd February, 2019 for Presidential and National Assembly while the Governorship, State House of Assembly and the FCT Area Council Elections is to hold on 9th March, 2019. pic.twitter.com/6zhvBLQe2a — INEC Nigeria (@inecnigeria) February 16, 2019

A government official said: “The legitimacy of the entire process will be questioned and the winner could lack the moral authority to superintend the affairs of the state.”

In the lead up to the election Nigeria has been dealing with pockets of instability. Authorities bolstered security in much of the country on the eve of the vote, after past elections were marred by violence, voter intimidation and ballot rigging.

A faction of Boko Haram attacked a state governor’s convoy on Tuesday, killing four people and stealing vehicles. Elsewhere, 15 people were crushed to death at a ruling party rally in eastern Port Harcourt. On Thursday, 14 sacks of ballot papers were intercepted in Kano state – though police said they were merely “specimen” papers to educate voters.