Niamey - Niger's opposition warned there would be no easy victory at the polls for incumbent Mahamadou Issoufou despite his vow of a first-round "knockout" blow, as voting wrapped up on Monday.
Voting was extended for a second day after several cities did not receive their ballot papers on Sunday.
"All the polling stations are closed," the vice-president of the independent national electoral commission (Ceni), Kadri Sanda Oumarou, told AFP late Monday.
Results are expected to be announced in around five days, officials said.
And the opposition said it is anticipating a run-off vote.
"There will be a second round," said a spokesman for former premier Seini Oumarou, one of the leading opposition candidates.
Known as the "Zaki" or "Lion" in Hausa, the majority language in Niger, Issoufou is seeking a second five-year term.
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In an interview with AFP last week, the 63-year-old leader said he was "absolutely" confident of a swift victory in the first round of the poll.
"If (Issoufou's) knockout blow fails, that will be a victory for us and a setback for him, because he made a point" of pledging a quick outright win, said Oumarou's spokesman Moussa Harouna.
Should he fail to win in the first-round, his rivals, who have accused him of planning to rig the result, have agreed to unite behind whoever scores highest among them for the run-off vote.
In the capital Niamey, long a bastion of jailed former prime minister Hama Amadou, several sources said he picked up the most votes in Sunday's first round.
Anadou campaigned for the election from behind bars after being arrested in November over his alleged role in a baby-trafficking scandal.
"As promised, he will go from prison to the presidency," a spokesman for Amadou said.
"The results are beyond our expectations. We aren't just confident: we are very, very, very confident".
On Sunday, polling stations stayed open late into the night due to voting delays.
After ballot papers failed to be delivered in some areas on time, voting took place for a second day in parts of the vast nation, such as Agadez in the north, southern Zinder and Tahoua in the west.
Oumarou's spokesman Harouna accused the national election commission of "doing a bad job", adding: "We are waiting for the reports from representatives on the ground... but the constitutional court will have work to do."
In Bosso in the southeast, armed men tried to take control of polling stations, he claimed.
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Interior Minister Hassoumi Massaoudou lashed out at the opposition's allegations.
"The elections are free and transparent. The proof of this is the fact that the opposition is ahead in Niamey. If we wanted to stage a hold-up, why wouldn't we have done so in Niamey?" Massaoudou said.
"They're talking nonsense. We're going to win a legitimate victory."
Though blessed with an abundance of uranium, coal and oil, Niger is one of the poorest nations on the planet.
A total of 7.5 million people were eligible to vote across the country on the edge of the Sahara desert, where security is a growing concern after attacks by jihadists from neighbouring Nigeria, Mali and Libya.