LAGOS - Nigeria slowly counted more results on Monday after a tight election for the presidency of Africa's most populous nation as delays and accusations of manipulation fuelled tensions.
Nearly 90 million were eligible to vote on Saturday for a successor to President Muhammadu Buhari, with many hoping for a new leader to tackle insecurity, economic malaise and widening poverty.
Voting on Saturday was mostly peaceful, but thugs ransacked some polling stations and many others opened very late in Lagos and other cities. Many voters stayed overnight to watch over the initial count at polling stations.
The election pits former Lagos governor Bola Tinubu, 70, of the ruling All Progressives Congress (APC) against former vice president 76-year-old Atiku Abubakar, of the Peoples Democratic Party (PDP).
But for the first time since the end of military rule in 1999, a surprise third-party candidate, Labour Party's Peter Obi, has challenged APC and PDP dominance with an appeal to younger voters.
Announcing first results state by state, Independent National Electoral Commission (INEC) on Sunday said APC's Tinubu won small, southwestern Ekiti state with PDP coming second.
INEC was due to announce more state by state results on Monday at 1000 GMT, but final tallies for the presidential race could take days.
Votes are tallied by hand at local polling stations and results are uploaded online to INEC's central database IReV, which is meant to improve transparency.
But slow uploading of results to INEC's website has fueled worries of malpractice in a country with a history of ballot rigging and vote buying.
By Monday morning, results from around 52,000 centres had been submitted to the platform from around 176,000 polling centres nationwide -- around 30 percent.
PDP on Monday accused the ruling APC governors of pressuring INEC over results in southeast and in parts of Lagos, a highly contested state with the most registered voters at more than seven million.
"APC is doing all in its means to cheat in Lagos," PDP spokesman Dele Momodu told reporters.
- Malpractice fears -
The early result in one state for APC's Tinubu was very preliminary in a country almost equally divided between a mostly Muslim north and a predominantly Christian south and with three main ethnic groups in different regions.
Voting is usually determined by large key states such as Lagos and northwestern Kano and Kaduna.
To win the presidency, a candidate must get the most votes, but also win at least 25 percent of votes cast in two-thirds of Nigeria's 36 states to reflect broad representation.
Nigeria's police force on Monday urged presidential candidates to "caution their party stalwarts and supporters to avoid making inciting comments."
When he was defeated by Buhari in the 2019 election, PDP's Abubakar claimed massive fraud, but the Supreme Court eventually rejected his challenge.
Labour Party chairman Julius Abure also accused election officials of failing to upload results from parts of Lagos and southern Delta State to benefit APC's candidate.
APC has said rival parties are just trying to undermine confidence in INEC.
But INEC said problems with uploading results on its IReV data page were due to "technical hitches" and there was no risk of tampering.
"The commission wishes to assure Nigerians that the challenges are not due to any intrusion or sabotage of our systems," it said.
- Competitive race -
The vote in Africa's biggest democracy is being closely watched elsewhere in a region battered by coups in Guinea, Burkina Faso and Mali and growing Islamist militancy.
Tinubu and Abubakar are old guard figures who have fought off past corruption accusations, but the emergence of Obi -- a Christian ethnic Igbo from the southeast -- threw the race open.
The race has some analysts forecasting a runoff between the two frontrunners if no candidate meets election requirements -- a first in Nigeria's history. It would have to be organised within 21 days.
Buhari, a former army general first elected in 2015, will step down after two terms in office. His critics say he failed in his key promises to make Nigeria safer.
Whoever wins the election must quickly get to grips with Africa's largest economy and top oil producer, beset by problems from a grinding jihadist war in the northeast to double-digit inflation.
By By Camille Malplat With Louise Dewast In Port Harcourt