A knife-wielding man has killed four staff at police headquarters in central Paris, French media report.
The attacker, who has not been named but is also said to be an employee there, was later shot dead by police.
There has been no official statement so far. The area in the île de la Cité – in the centre of Paris – has been sealed off.
The attack comes a day after police went on strike across France over increasing violence towards officers.
It happened at about 13:00 local time (11:00 GMT; 12:00 BST) in the courtyard of the building.
President Emmanuel Macron, Prime Minister Edouard Philippe and Interior Minister Christophe Castaner have all gone to the site.
Paris Mayor Anne Hidalgo confirmed on Twitter that “several people” had been killed in the attack, which took place near major tourist sites including the Notre-Dame cathedral.
Three men and one woman were killed in the attack, according to French broadcaster BFMTV.
Another person was also reportedly wounded.
According to French media, the attacker was a 45-year-old man who had worked in an administrative capacity for the Paris police force for 20 years.
They said he had been working in the police force’s intelligence division.
BFMTV reports that he stabbed two people inside two offices, one person on a stairway and the fourth person inside the building’s courtyard – where the knifeman was shot dead.
“Police were running around in panic,” an eyewitness who was inside the courtyard at the time of the attack told Le Parisien newspaper.
“I was surprised to hear shooting because this is not a place where you hear that kind of thing. I first thought it was a suicide because there are a lot of those at the moment,” he added.
