Nigeria's main opposition has claimed victory in the country's tense general election as former military ruler Muhammadu Buhari pulled ahead of President Goodluck Jonathan in the vote count.

If confirmed, it would be the first democratic change of power in the history of Africa's most populous country.

With 32 out of 37 results in, Buhari's All Progressives Congress (APC) had won 19 states with Jonathan's Peoples Democratic Party (PDP) on 12 plus the Federal Capital Territory of Abuja.

Asked if the APC was claiming victory over the PDP, party spokesman Lai Mohammed told AFP: "Yes".

"This is the first time the opposition has voted a government out of power in Nigeria's history," he added.

Buhari, 72, stretched his lead to nearly 2.9 million votes over 57-year-old Jonathan, with most of the remaining states in the opposition candidate's northern heartland.

They included the northeastern states hit hardest by the six-year Boko Haram insurgency.
The former military ruler won the key prize of Lagos in the southwest but at one point his lead was cut to 500,000 votes after landslide victories for Jonathan in his southern Delta homeland.

The vote pitting Jonathan against Buhari was the closest election contest ever in Africa's biggest economy which has a population of 173 million.

The opposition leader, making his fourth run at the presidency, has been buoyed by frustration over endemic corruption, criticism over Jonathan's handling of Boko Haram and a stronger opposition.

The PDP and the APC on Sunday traded allegations of vote rigging and other irregularities, raising the possibility of a legal challenge to the results.

Violence has often flared in previous Nigerian elections after the winner is announced and the United States and Britain warned against any "interference" with the count.