A third-party candidate in Nigeria's tightly contested presidential election has caused a major upset by winning in its biggest city, Lagos.

The Labour Party's Peter Obi narrowly defeated the ruling party's Bola Tinubu in his heartland, results announced by state election officials show.

This is the first time since 1999 that a party backed by Mr Tinubu, a two-time Lagos governor, has not won the state.

But Mr Tinubu has won three of the five other states declared so far.

 

He also won in his south-western strongholds of Ondo, Ekiti and Kwara, narrowly losing to Atiku Abubakar of the main opposition Peoples Democratic Party (PDP) in Osun state.

Mr Abubakar has also narrowly won the presidential election in Katsina, the home state of outgoing President Muhammadu Buhari.

 

But with 30 states and the capital, Abuja, still to declare, it remains far too soon who might be elected Nigeria's next president.

The results from Ekiti, Kwara and Osun have all been confirmed by the head of the Independent National Electoral Commission (Inec) at its headquarters in the capital, Abuja, however the other results remain provisional.

The delays in getting results from the states and the capital, Abuja, have led to growing frustration.

The electoral commission has apologised for the unresponsiveness of the results viewing page on its website, saying a surge in use caused technical hitches.

The delays are partly a result of the election continuing for a second day in parts of the country.

The election on Saturday saw voting start several hours late in many areas, and also attacks on some polling stations.

 

More than 87 million people were eligible to take part, making it the biggest democratic exercise in Africa.

The ruling All Progressives Congress (APC) and the PDP have dominated Nigeria since the end of military rule in 1999 but this time, Mr Obi from the previously little known Labour Party is expected to mount a strong challenge to the two-party system. He has the support of many young people, who make up a third of registered voters.

A candidate needs to have the most votes and 25% of ballots cast in two-thirds of Nigeria's 36 states to be declared the winner.

Otherwise, there will be a run-off within 21 days - a first in Nigeria's history.

Why have results been slow in coming?

The earliest a winner has been announced is on the third day after voting in the previous two elections, but many had expected a faster conclusion this time because of the introduction of an electronic result transmission system.

This was meant to increase transparency and make sure the results could not be altered by creating a digital version on the website of the electoral commission, Inec.

 

But many voters have accused electoral officials of refusing to upload the results at the polling units as they are supposed to.

Officials complained of a lack of internet in some places to upload the results, but voters have shared videos and images shared where Inec officials refused to upload the results.

There have also been reports of disturbances at Inec collation centres in some states, with some political parties on Sunday asking their supporters to go to such places to protect their votes.