Abuja, Feb 27 (AFP) Muhammadu Buhari was re-elected Nigeria's president, results showed Tuesday, after a delayed poll that angered voters and led to claims of rigging and collusion.

Buhari, 76, took an unassailable lead of more than four million votes as the last states were yet to be declared, making it impossible for his nearest rival, Atiku Abubakar, to win.

The win was confirmed as Abubakar won in the very last state to declare -- Rivers in the south -- but could not claw back the deficit.

Supporters of Buhari's All Progressives Congress (APC) gathered at his campaign headquarters in the capital, Abuja, to celebrate even before the final results were announced.

Some sang "We're popping champagne!" while Vice-President Yemi Osinbajo was seen in a video clip singing "Up we go!" in a reference to Buhari and his "Next Level" campaign slogan.

Buhari's spokesman, Garba Shehu, posted a photograph of the president on Twitter, watching the results on television. "#BuhariHasWon," he wrote.

But there were none of the spontaneous street parties that marked his victory four years ago, when he became Nigeria's first opposition candidate to beat an incumbent president.

To win the presidency in Nigeria, a candidate needs a majority of votes nationwide and at least 25 per cent of support in two-thirds of Nigeria's 36 states and the FCT (Federal Capital Territory).

Initial results showed Buhari won 15,191,847 votes or 56 per cent of the vote while Abubakar, of the Peoples Democratic Party (PDP) won 11,262,978 votes or 41 percent.

Buhari won in 19 states -- including the two most populous, Lagos and Kano -- while Abubakar was victorious in 17 states and the FCT.

In 2015, president Goodluck Jonathan won plaudits for conceding to Buhari in a phone call, as the results indicated he could not win.

"Nobody's ambition is worth the blood of any Nigerian. The unity, stability and progress of our dear country is more important than anything else," he said at the time.

Previous elections have been marked by political violence, including in 2011, when more than 800 people were killed.

There was no immediate official concession from Abubakar, whose party earlier Tuesday called on the electoral commission to halt the count, citing irregularities.

The election, which was delayed just before polls were due to open on February 16.

The electoral commission cited logistical difficulties in delivering ballot materials. (AFP)

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