Members of Nigeria's main opposition party voted through the night to choose a candidate to challenge President Goodluck Jonathan at next year's elections, with a result expected later on Thursday.
Proceedings at the All Progressives Congress (APC) presidential primary at a stadium in the financial capital Lagos had been due to get under way mid-afternoon on Wednesday.
But it did not start until gone 11:00 pm (2200 GMT) and the 7,214 delegates only began to cast their ballots -- alphabetically by state -- from 3:00 am.
The primary is expected to be a two-horse race between Nigeria's former military ruler Muhammadu Buhari and Atiku Abubakar, who was vice-president for eight years from 1999.
The ruling People's Democratic Party (PDP) formally endorsed Jonathan at a separate meeting in the capital, Abuja late on Wednesday. He was the only candidate.
Jonathan, in power since 2011, said he was honoured to have been chosen to run for a second term, which he said would build on the work of his first and make security "the utmost priority".
The head of state said the security situation in the northeast, where Boko Haram militants have been waging an insurgency since 2009, was "improving a little".
He also expressed hope that next February's elections will be held countrywide, after concern that violence would largely prevent voting in the three worst-affected states.
Jonathan chose current vice-president Namadi Sambo as his running mate.
The APC -- a coalition of four opposition parties -- is seen as having its best chance of seizing power from the PDP since civilian rule returned to Nigeria in 1999.
It has been campaigning against Jonathan's record on tackling Boko Haram, the PDP's stewardship of the economy and also its perceived inability to tackle corruption and impunity.