(AFP) - Nigerians waited anxiously for first results on Sunday after a tight presidential election among three frontrunners that has energised Africa's most populous nation, where many long for change.

The voting was carried out mostly peacefully, despite some ransacked polling stations and long delays. Voters stayed up late at night in many locations to observe the count and "protect" the ballots.

Nearly 90 million were eligible to vote on Saturday for a successor to President Muhammadu Buhari, with many Nigerians hoping a new leader will do a better job tackling insecurity, economic malaise and growing poverty.

"Everything will change. Nigeria will become a better place," said driver Samuel Ijeagha, 56, voting in southeast Anambra State. "Everything is not normal, but with the election, everything will become normal again."

Independent National Electoral Commission (INEC) Chairman Mahmood Yakubu told reporters results would be officially announced state by state from around 1700 GMT on Sunday when tallies are collated at its Abuja headquarters.

But slow uploading of results to INEC's online website stirred up worries of electoral malpractice in a country with a history of ballot rigging and vote buying.

"Let Nigeria decide O! @inecigeria," Nigerian Afrobeats star and Grammy Awards winner Burna Boy wrote on Twitter. "No try any result magic."

The election pits former Lagos governor Bola Tinubu, 70, of the ruling All Progressives Congress (APC) against former vice president Atiku Abubakar, of the Peoples Democratic Party (PDP), 76.

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 the APC and PDP dominance with a campaign message of change.

Spread over more than 176,000 polling stations, voters also cast their ballot on Saturday for Nigeria's two houses of parliament, the House of Representatives and Senate.

Observers group Yiaga Africa said it was "deeply concerned with the delay" in results.

"If the official results are manipulated at any point in the process we will be able to expose it," said Hussaini Abdu of Yiaga Africa on Sunday.

- 'Ready for the challenge' -

In Lagos and other cities, crowds stormed polling stations late on Saturday as electoral officials tallied the first results by hand and read out the counts before transmitting them to a central database.

"We just finished counting, but we need to make sure they upload the results," said Chizoba Onuoha, an IT manager, watching the count at her Lagos polling station on Saturday.

On Sunday morning, people gathered at a newspaper stand in the Falomo area of Lagos, eager for results to come in.

"We are very happy this morning because we have witnessed one of the most peaceful elections in Nigeria," said 27-year-old mechanic Orubibi Dighobo.

In the southern oil hub of Port Harcourt, a dozen people were still at their polling unit after the counting had finished on Saturday, shouting at the electoral official to destroy unused ballots.

Nearby, at Rumuepirikom Civic Centre where electoral staff from 78 polling units were gathered to upload results online, frustrations were growing.

"There is no network," said an election volunteer, while others were starting to fall asleep on tables and chairs.

The commission has 14 days to officially announce results, but an online tally could be made available over the next few days.

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.

Lagos has the most registered voters at more than 7 million, followed by two states in the country's mostly Muslim north, Kano and Kaduna states.

The competitive race has some analysts forecasting an unprecedented runoff between the two frontrunners if no candidate meets election requirements. It would have to be organised within 21 days.

- Old guard rivals -

The success of Nigeria's vote will be closely watched in West Africa, where coups in Mali and Burkina Faso and growing Islamist militancy have taken democracy in the region back a step.

Buhari, a former army general, will step down after two terms in office. His critics say he failed in his key promises to make Nigeria safer.

Fuel and cash shortages caused by a bank note exchange in the run-up to the election also left many Nigerians struggling more than usual in a country already hit by more than 20-percent inflation.

APC's candidate Tinubu, a long-time political kingmaker and southern ethnic Yoruba Muslim, says "It's my turn" for the presidency. He says his experience as Lagos governor will count.

He faces a familiar rival -- PDP candidate Abubakar, a Muslim from the northeast who is on his sixth bid for the top job and touts his business experience to fix the economy.

But both are old guard figures who have fought off past corruption accusations, and the emergence of Obi, a Christian ethnic Igbo from the southeast, threw the race open.

© Agence France-Presse