Gunshots reported outside historic Notre Dame cathedral in Paris

"I heard two shots and saw a man lying on the ground in a pool of blood", he said.

A man, upper left, who attacked a police officer, lies wounded on the esplanade of Notre Dame cathedral in Paris.

Farid Ikken, 40, of Algerian origin, has been identified as the attacker who emerged from a crowd of tourists yesterday afternoon and swung his weapons at three police officers.

The minister visited the prefecture of police, 50 metres from the scene of the attack, to talk to officers involved in the incident.

The Paris prosecutor's office swiftly launched a counter-terrorism investigation into the attack, the first since President Emmanuel Macron won power last month and days before the first round of a parliamentary election in France.

One officer has minor injuries, the BBC reports, while the assailant has been hospitalized.

Soderberg tweeted a photo from inside the Notre Dame showing those locked inside putting their arms in the air as instructed by police.

Several hundred people were held inside Notre Dame Cathedral after a man went after officers patrolling outside the Paris landmark.

Among the people ordered to remain inside the cathedral was former U.S. ambassador to the United Nations Nancy Soderberg. "We had no idea if there were any accomplices inside", she told Associated Press. The square in front of the cathedral was evacuated.

Around 1,000 visitors were kept inside Notre Dame for more than an hour until police determined the threat had passed. "We were trying to figure out what was going on", he said.

Paris police investigate in Notre Dame attack; suspect used hammer to attack police officer outside cathedral.

France is still under a state of emergency imposed after the deadly November 2015 terrorist attacks in Paris.

Police swiftly converged on the area, shouting at passersby to stay back. French authorities say there have been 50 terror plots uncovered in the country over the past three and a half years, Fox News reported.

Authorities said the situation was under control, and the attacker was taken to a hospital.

"These are the kind of attacks that are, that give everybody nightmares, because there's no plot", he said. His motives remain unclear but he seemed to be acting by himself and it didn't seem like a very well planned attack.

There have been various smaller attacks since, often targeting security forces.