Niger's President Mahamadou Issoufou enjoyed a strong lead in his bid for a second term as leader of the West African nation, according to partial results.
With 3.18 million votes from Sunday's election counted - representing a little over 40 percent of the 7.5 million-strong electorate - the 63-year-old incumbent had just over 46 percent.
The partial result showed that he was well ahead of his closest rival, detained former parliamentary speaker Hama Amadou, whose supporters said the poll was rigged.
Amadou is behind bars on baby trafficking charges he says were concocted to thwart his presidential ambitions.
The partial count showed that he garnered just over 16 percent, while former Prime Minister Seini Oumarou, had about 11 percent, the electoral commission said.
Issoufou's aides told AFP news agency that they were confident the man nicknamed the "Lion" would make good on his promise to deliver a "knockout blow" to his opponents in the first round.
They said that ballots still being counted in his western stronghold of Tahoua were likely to tip him over the 50 percent score needed to avoid a runoff.
The final score could be announced later on Thursday, electoral officials said. Turnout in the areas that have announced results so far was more than 67 percent.
The opposition has on Tuesday already said it will not recognise the result, declaring the election rigged in Issoufou's favour.
"Clearly, everything has been organised for a first-round win [by Issoufou]. The official results have yet to be announced but it's so obvious," Amadou Boubacar Cisse, one of his challengers, said on Thursday.
A total of 15 candidates ran for president of the vast country on the edge of the Sahara Desert, which has been rocked over the past year by attacks by Boko Haram fighters operating out of neighbouring Nigeria.
Voters also cast ballots for members of parliament.
The African Union, which deployed 40 observers, said that it was generally satisfied with the organisation of the vote despite delays in some areas caused by logistical glitches.