Nigeria's presidential and parliamentary elections have been delayed for a week.
The Independent National Electoral Commission (INEC) made the announcement just five hours before the polls were due to open on Saturday.
"Proceeding with the election as scheduled is no longer feasible," commission chairman Mahmood Yakubu said, citing logistical issues.
The vote has been rescheduled for Saturday 23 February.
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The announcement came after an emergency meeting at the INEC headquarters in the capital, Abuja.
Why have elections been postponed?
Mr Yakubu said the decision was made following a "careful review" of the election "operational plan", adding that there was a "determination to conduct free, fair and credible elections".
He said the delay was necessary to give the commission time to address vital issues and "maintain the quality of our elections", but did not provide further details.
In the past two weeks several INEC offices have been set alight, with thousands of electronic smart card readers and voter cards destroyed.
There have also been claims of shortages of election material in some of the country's 36 states.
Nigeria has been forced to bolster its security, with the run-up to the elections marred by violence.
On Friday, officials in north-west Nigeria reported the discovery of the bodies of 66 people, 22 of them children and 12 women, killed by "criminal elements".
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
How important is this poll?
The future of Africa's most populous nation and largest economy is at stake.
Whoever wins will have to address power shortages, corruption, security problems and a sluggish economy.
There are 73 registered candidates in the presidential election, but campaigning has been dominated by President Muhammadu Buhari, 76, and his main challenger, former Vice-President Atiku Abubakar, 72.
Mr Buhari says he has built a strong foundation for prosperity, but his rival says Nigeria is not functioning.