Provisional results from 38 out of 266 constituencies showed that Bazoum was in a comfortable lead, winning a 54.1% share of votes counted so far against his main challenger and former president Mahamane Ousmane, according to Niger's electoral commission.

Nigeriens went to the polls on Sunday in the second round of the country's presidential election. The runoff between the two political heavyweights is expected tol pave the way for Niger'sfirst democratic transition of power since independence from France more than six decades ago.

Ousmane, who took nearly 17% of the vote in the first round, can count on the support of a coalition of 18 opposition parties as well as Hama Amadou, previously thought to be the most formidable candidate against Bazoum. But Amadou was banned from running because of a conviction for baby trafficking which he has slammed as politically motivated.

Several dead in vehicle blast

As voting came to an end, at least seven people were killed and three more were seriously injured when a vehicle belonging to the electoral commission hit a landmine.

The blast took place in the rural commune of Dargol in Tillabery region, some 100 kilometers (60 miles) from Niger's capital Niamey in the so-called tri-border region where Niger, Mali and Burkina Faso converge. 

"This is a painful moment. It is a great shock for us, for us all," said Interior Minister Alkache Alhada. 

Addine Agalass, an advisor to the governor of Tillabery, told The Associated Press by phone, "It's unclear if it was intended to target the electoral commission officials or if it was related to the election."

A new dawn for Niger

The vote was called after outgoing President Mahamadou Issoufou announced he was voluntarily stepping down after two five-year terms. 

"I'm proud to be the first democratically elected president in our history to be able to pass the baton to another democratically elected president," said Issoufou as he voted in Niamey. 

Thousands of soldiers were deployed, to ensure a peaceful transfer of power. Election results are expected in several days. 

The two candidates vying to replace Issoufou are political stalwarts in the West African nation, which is one of the poorest in the world.

Mohamed Bazoum, Issoufou's right-hand, is widely seen as the favorite after winning 39.3% of the vote in the first round. He has vowed to continue Issoufou's policies, with a focus on security and revamping the economy. He has the backing of the candidates who came third and fourth in the first round.

Mahamane Ousmane, was Niger's first democratically elected president in 1993 until he was toppled in a coup three years later. He won 17% of the votes in the first round and has the endorsement of about a dozen smaller parties and candidates. He has vowed to implement change and tackle corruption.

Ousmane also expressed concerns about electoral fraud and stressed that Nigeriens are "no longer willing to tolerate rigged elections." 

"The suffrage of the citizens must be respected," Ousmane told reporters after he voted in the city of Zinder. "If citizens ever find out that these elections have been rigged again, I fear that the situation will be difficult to manage," he added.

Relative 'calm' in southeast Niger

Magagi Ganda Aissa, a Niamey-based civil society member, said she was "not aware" of any incidents of voting fraud in Niger's largest city, "There have been reports that armed people have arrived and seized ballot boxes in the interior of the country," she added.

According to DW correspondent Marah Mahamadou, election day Diffa in the southeast, along the border with Nigeria , was calm. 

"We must admit that the vote went very calmly. At the beginning, there was a little fear, but nothing was reported. People everywhere went out to vote," she said.

What challenges do they face?

The Sahel nation has a population of 24 million and struggles with poverty, recurring drought, floods and two festering insurgencies. Militants linked to al-Qaida and the "Islamic State" (IS) armed group have carried out a series of attacks near Niger's western border with Mali and Burkina Faso, while Boko Haram has killed hundreds of people along the southeastern border with Nigeria.

One of Niger's few exports, uranium, has been hit by a drop in price in recent years, and the coronavirus pandemic has weighed on Niger's economy.

Political analyst Elhadj Idi Abou, based in Niamey, said the result could go either way and that turnout was expected to be high.

"For me, there is no favorite because this ballot is the most open and the outcome does not depend on alliances but on the citizens. Both candidates have the same chances," he told the Reuters news agency.

Niger is the poorest nation in the world, according to the United Nations' development rankings for 189 natons. In the country with a population of roughly 23 million and the highest birth rate in the world, 7.4 million are eligible to vote. 

Eric Topona and Sandrine Blanchard contributed to this article.