Nice’s mayor, Christian Estrosi, who described the attack as terrorism, said on Twitter it had happened in or near the city’s Notre Dame church and that police had detained the attacker.

Estrosi said the attacker had shouted the phrase “Allahu Akbar”, or God is greatest.

One of the people killed inside the church was believed to be the church warden, Estrosi said.

​ The attacker kept shouting “Allahu Akbar” even after he had been detained, Estrosi said.

​ “The suspected knife attacker was shot by police while being detained, he is on his way to hospital, he is alive,” Estrosi told reporters.

“Enough is enough,” Estrosi said. “It’s time now for France to exonerate itself from the laws of peace in order to definitively wipe out Islamo-fascism from our territory.”

Police said three people were confirmed to have died in the attack and several were injured.

A police source said a woman was decapitated. French politician Marine Le Pen also spoke of a decapitation having occurred in the attack.

Estrosi said the victims had been killed in a “horrible way”.

“The methods match, without doubt, those used against the brave teacher in Conflans Sainte Honorine, Samuel Paty,” he said, referring to a French teacher beheaded earlier this month in an attack in a suburb of Paris.

Estrosi said a woman had tried to escape from inside the church and had fled into a bar opposite the building.

The French anti-terrorist prosecutor’s department said it had been asked to investigate the attack.

Reuters journalists at the scene said police armed with automatic weapons had put up a security cordon around the church, which is on Nice’s Jean Medecin avenue, the city’s main shopping thoroughfare. Ambulances and fire service vehicles were also at the scene.

The attack comes while France is still reeling from the beheading earlier this month of French middle school teacher Paty by a man of Chechen origin.

The attacker had said he wanted to punish Paty for showing pupils cartoons of the Prophet Mohammad in a civics lesson.

It was not immediately clear if Thursday’s attack was connected to the cartoons, which Muslims consider to be blasphemous.

Since Paty’s killing, French officials – backed by many ordinary citizens – have re-asserted the right to display the cartoons, and the images have been widely displayed at marches in solidarity with the killed teacher.

That has prompted an outpouring of anger in parts of the Muslim world, with some governments accusing French leader Emmanuel Macron of pursuing an anti-Islam agenda.