Rioters burned at least eight churches in Niamey on Saturday in protest at the depiction of the Prophet Mohammed on the cover of France's Charlie Hebdo weekly, AFP reported.
It was the second day of violence in the west African country over the Mohammed cartoon, after five people were killed and 45 injured in protests in Niger's second city of Zinder on Friday.
The death toll went from four to five after a body was found "burned inside a church", said Niger's President Mahamadou Issoufou.
Bars, hotels and various businesses under non-Muslim ownership or bearing signs of French companies were also targeted on Saturday.
French Foreign Minister Laurent Fabius, whose country has defended the Charlie Hebdo cover as freedom of expression, condemned "the use of violence, today in Niamey and yesterday in Zinder".
About six groups of 200 to 300 protesters were believed to be rampaging through Niamey, a security source said.
"As soon as the protesters started toward the grand mosque we knew this was coming," said Kiema Soumaila, manager of the Toulousain, a well-known bar in Niamey.
"They burned everything after smashing anything that was glass on the road," Soumaila added.
Muslim elder Yaou Sonna, speaking on behalf of around 20 of his peers, called for restraint, saying on state television: "Don't forget that Islam is against violence. I urge men and women, boys and girls to calm down."
Around 100 helmeted riot police stood in front of the Niamey cathedral at midday, protecting it from a crowd of stone-throwing youths.
Police had used tear gas earlier in the day to disperse a crowd of about 1,000 young people massed in front of Niamey's grand mosque who were armed with iron bars and clubs.
France's embassy in its poverty-stricken former colony warned French citizens to stay indoors after rioters ransacked several French-linked businesses, including telephone kiosks run by Orange.
The satirical weekly Charlie Hebdo has repeatedly published cartoons of Mohammed over the years and its latest issue, released on Wednesday, features a cartoon of Mohammed on its cover holding a "Je Suis Charlie" (I Am Charlie) sign under the headline "All Is Forgiven".
It came a week after attacks by three Islamists on its offices, a kosher supermarket and a policewoman left 17 people dead in and around Paris over three days, deeply shocking the country and sparking an outpouring of international support.
Many Muslims see any depiction of Islam's prophet as offensive, while many Western governments have defended Charlie Hebdo's right to freedom of expression.
Unmarked grave for Charlie Hebdo attacker
Meawhile, one of the brothers who launched a deadly attack against the French satirical magazine Charlie Hebdo earlier this month has been buried in an unmarked grave.
Said Kouachi was buried secretly yesterday in the eastern city of Reims, where he had lived before the attack.
The city's mayor said he had opposed the burial, fearing the grave could become a shrine, but had been forced to accept it by law.
Two days after attacking the magazine and killing 12 people, Kouachi and his younger brother Cherif were killed by the police at an industrial estate north of Paris.
Cherif Kouachi is expected to be buried in his home town of Gennevilliers outside Paris.