Paris: A police officer shot and wounded an assailant armed with a hammer and knives on the square outside Notre Dame Cathedral in Paris on Tuesday afternoon, local authorities said.

The cathedral, a Gothic landmark on the Seine River, was sealed off, and visitors and worshippers were told not to leave. The square in front of the cathedral was evacuated. The officer was wounded, and the attacker was taken to a hospital, police said.

The Paris prosecutor's office said it had opened a terrorism investigation and confirmed that the man had attacked the police officer with a hammer. He also had two knives with him, the office said.

The officer was lightly wounded, the prosecutor's office said, adding it was still unclear whether more than one officer opened fire.

On Twitter, the authorities said that a police operation was underway and that people should avoid the area.

About 900 people were inside Notre Dame when the shooting occurred, Karine Dalle, the press officer for the Paris archdiocese, said in a text message, adding that they were "sitting calmly" and had been told about the event. Two auxiliary bishops were present as well, she said, and were reassuring the crowd. She said there was no panic inside the cathedral.

Tourists visiting the historic cathedral tweeted they were shut inside the building immediately after the incident.

Three major terrorist attacks in France, in January and in November in 2015, and in July 2016, claimed more than 230 lives, and the country remains under a state of emergency.

Landmarks across France, the world's most-visited country, are considered especially vulnerable, despite constant policing.

In February, a 29-year-old man armed with two large knives and shouting "God is great" in Arabic lunged at a military patrol near an entrance to the Louvre in Paris and slashed a soldier. He was shot by a soldier.

New York Times