The incident took place inside the church at about 9am local time. At least two people have died in the attack and several others have been injured. The incident is believed to be terror-related, according to the city’s mayor.
The suspect was promptly arrested by police and is believed to have been shot.
A security perimeter has been set up around the church, located in the city center.
Witnesses on social media have reported hearing shots fired as armed police search the area.
People have been evacuated from the scene.
National Police have urged people to avoid the area and said there is no need to panic.
The Mayor of Nice has said he suspects the incident is terror-related.
He wrote on Twitter: “I am on site with the @PoliceNat06 and the @pmdenice who arrested the perpetrator of the attack.
“I confirm that everything suggests a terrorist attack in the Basilica of Notre-Dame de #Nice06.”
Gérald Darmainin, France’s interior minister, has said he is chairing a crisis meeting into the incident.
He wrote on Twitter: “#Nice : a police operation is in progress.
“Avoid the area and follow the instructions. “After having had the mayor of Nice @cestrosi, I am chairing a crisis meeting at the Ministry of the Interior.”
More to follow…
Additional reporting by Maria Ortega