Nigeria's electoral watchdog on Saturday postponed presidential and parliamentary elections for one week, just hours before polls were due to open.
The country's two main political parties swiftly condemned the move and accused each other of orchestrating the delay as a way of manipulating the vote.
Voting had been due to start at nearly 120,000 polling stations in Africa's most populous nation at 0700 GMT, with a record 73 candidates on the ballot.
TRT World's Narkwork Kwabla reports.
President Muhammadu Buhari, 76, was set to seek a second term of office against a stiff challenge from the main opposition candidate, former vice president Atiku Abubakar, 72.
But rumours began circulating late on Friday about a possible postponement after widespread reports of problems with the delivery of election materials, including ballot papers.
Members of the Independent National Electoral Commission (INEC) met in emergency session in Abuja and after examining the logistics plans concluded the timetable was "no longer feasible", commission chairman Mahmood Yakubu said.
"Consequently, the commission has decided to reschedule to Saturday February 23, 2019," he told reporters.
Parliamentary elections for 360 seats in the lower House of Representatives and 109 seats in the Senate will be held on the same day.
Governorship and state assembly elections will be pushed back to March 9, Yakubu said.
"This was a difficult decision for the commission to take but necessary for the successful delivery of elections and the consolidation of our democracy," he added.
Buhari's campaign spokesman Festus Keyamo, for the governing All Progressives Congress, (APC) said the news was a "huge disappointment" and hit out at INEC for be ing unprepared.
Keyamo called on the body to remain impartial "as the rumour mill is agog with the suggestion that this postponement has been orchestrated in collusion with the... PDP".
For his part, Abubakar of the main opposition Peoples Democratic Party blamed the Buhari government for "instigating the postponement" but called on his supporters to remain calm.
"We will overcome this. You can postpone an election but you cannot postpone destiny," he added in a statement.
Nigeria has postponed voting before: in 2015, INEC announced a six-week delay just one week be fore the election, citing security concerns linked to the Boko Haram insurgency.
The six-week delay was seen as a way for president Goodluck Jonathan to claw back votes after a strong challenge from Buhari, then an opposition candidate.
The same argument may be made again, with little to separate Buhari and Abubakar.
Rescheduling could also prove a headache for voters who travelled to their home states. Whether they are able to do so again - or would want to - will be closely watched.
The main candidates had also returned to cast their ballot - Buhari to the northwest state of Katsina, and Abubakar to Adamawa, in the northeast.
In many areas suffering intermittent electricity supply and poor road infrastructure, thousands of INEC agents had been working into the night to deliver election materials.
In Aba, in the southeast, hundreds of volunteers struggled to determine where they were to be deployed, on the eve of polling.
"I've been here 13 hours and I've still not seen my name on the lists. Where and how am I going to work tomorrow?" asked one woman.
Dozens killed in violence
Meanwhile, authorities in northwest Nigeria on Friday said police had discovered the bodies of 66 people, including women and children, in an area known for ethnic and religious clashes.
Kaduna state governor Nasir El Rufai said the grim find was made in eight villages in the Kajuru area, some 40 km southeast of the state capital, Kaduna city.
"Security agencies today reported the recovery of 66 bodies that were killed in attacks by criminal elements," he said in a statement.
"Among the victims were 22 children and 12 women. Four wounded persons rescued by the security agencies are now receiving medical attention.
"(The) government condemns the attacks and commiserates with the families of the victims."
There was no immediate comment from the police but El Rufai, a close ally of President Muhammadu Buhari, said officers had been sent and arrests made.
He urged community, traditional and religious leaders to warn local people not to launch reprisal attacks.
"The killings are being investigated and residents are assured that indicted persons will be prosecuted," he said.
Kaduna has long been a centre for deadly unrest, fuelled by long-standing ethnic and religious tensions, as well as election-related violence.
But Maisamari Dio, president of the ethnic Christian Adara community, which is dominant in the Kujuru area, blamed the killings on ethnic Fulani Muslims.
He told AFP Fulanis attacked a village on Sunday, killing up to 12 people. Angry Adara people mounted reprisals in recent days.
"The people found by the Kaduna state government today were likely those killed (by the Fulani) and some Adara, a mix, but I am not sure of the extent," he added.
"The situation in the last three years has been recurring, with kidnapping, killings, people being attacked.
These people will sometimes give advanced threats."
The announcement by El Rufai, who is seeking re-election, is unusual and a possible indication of deaths from both communities.
But his statement will also be designed to try to defuse anger.
Calls for peace
El Rufai's spokesman Samuel Aruwan said Kaduna residents should "uphold peace and harmony, shun violence and allow the elections to be held in an atmosphere of calm".
Hundreds of people were killed in 2011 when then-opposition candidate Buhari, a Muslim former military ruler from the north, lost to Goodluck Jonathan, a southern Christian.
Buhari stands for re-election. His main challenger is Atiku Abubakar, another ethnic Fulani Hausa-speaking Muslim, from northeast Nigeria.
Security is a major election issue, with no sign of an end to Boko Haram's insurgency in the northeast and renewed violence between farmers and herders in central states.
Northwest Nigeria – and particularly Zamfara state – is also in the grip of spiralling attacks by criminal gangs involved in cattle rustling and kidnapping for ransom.
Kaduna state borders Zamfara.
Local leaders in the Birnin Gwari region of Kaduna told AFP in January they suffered deadly attacks by armed bandits on an almost daily basis.