Ruling party candidate Mohamed Bazoum is seen by many as the favourite after leading in the first round on December 27 with 39.3 per cent of the vote.

He is up against former President Mahamane Ousmane, who scored 17 per cent.

Bazoum, a 61-year-old politician who had held several top positions in outgoing President Mahamadou Issoufou's governments including the foreign and interior ministries, is backed by the candidates who came third and fourth in the first round.

Bazoum has vowed to continue Issoufou's policies, making security a focal point as the West African country battles insurgencies, while introducing policies to revamp the economy.

Ousmane, 71, was Niger's first democratically elected president and was ousted in a 1996 military coup.

He has been endorsed by around a dozen smaller parties and first round candidates and has promised to bring change and tackle corruption.

The first vote was cast at a polling station in the capital Niamey about half an hour after the official 8 am start of voting on Sunday.

"I came to fulfill my civic duty for my country," said Djama Gado Harouna, a 66-year-old retiree, after casting her ballot.

"The start of the vote was transparent and we think that it will be throughout the day."

The Sahel nation of around 24 million is one of the poorest in the world and struggles with recurring drought and destructive floods.

The coronavirus pandemic has weighed on its economy, while weak prices for its main export, uranium, have hit revenues.

Australian Associated Press