An attacker armed with a knife killed three people at a church on Thursday in the Mediterranean city of Nice, authorities said.

It was the third attack in two months in France and comes when the country is still shaken by the beheading of a teacher in a Paris suburb this month by a young Muslim man after the teacher showed caricatures of the Prophet Muhammad in a class.

The assailant was wounded by the police and hospitalised after the killings at the Notre Dame Church, less than a kilometer from the site in 2016 where another attacker plowed a truck into a Bastille Day crowd, killing dozens.

Thursday's attacker was believed to be acting alone and police are not searching for other assailants, said two police officials, asking not to be named.

France's anti-terrorism prosecutor's office opened an investigation into the killings, which marked the third attack since the opening in September of a terrorism trial in the January 2015 killings at the satirical newspaper Charlie Hebdo and a kosher supermarket.

"He cried 'Allah Akbar!' over and over, even after he was injured," said Nice Mayor Christian Estrosi, who told BFM television that three people had died, two inside the church and a third who fled but was mortally wounded. "The meaning of his gesture left no doubt."

In Nice, images on French media showed the neighborhood locked down and surrounded by police and emergency vehicles. The police warned residents to stay away from the area around the church as a “very serious” event was underway and controlled explosives were being used. They also urged residents to remain calm as sounds of explosions could be heard as sappers exploded suspicious objects.

The lower house of parliament suspended a debate on France's new virus restrictions and held a moment of silence Thursday for the victims. The prime minister rushed from the hall to a crisis center overseeing the aftermath of the Nice attack.

French President Emmanuel Macron was headed to Nice later in the day.

In September, a man who had sought asylum in France attacked bystanders outside Charlie Hebdo's former offices with a butcher knife.