A knife-wielding employee has killed three officers and one administrative worker at police headquarters in the centre of the French capital, Paris.
The attacker, who has not been named, was shot dead by police.
Witnesses described scenes of panic, with many people fleeing the building in tears. The area in the île de la Cité was sealed off.
The attack came a day after police went on strike across France over increasing violence towards officers.
The Paris prosecutor said a murder investigation had been launched.
A motive for the attack remains unclear. However, police union officials have suggested the attacker may have been involved in a workplace dispute.
What happened?
At about 13:00 local time (11:00 GMT; 12:00 BST), the attacker is said to have gone into the building and straight to his office where he began attacking colleagues with a knife.
He stabbed three people inside two offices and two women on a stairway, before he was shot dead by an officer inside the building’s courtyard, according to French media.
There were tensions between the knifeman and his supervisor, according to police union official Christophe Crepin.
“I do not think this is a terrorist act,” Mr Crepin, who knew the attacker, told Franceinfo Radio.
Police union leader Jean-Marc Bailleul described it as a criminal act, telling BFMTV: “It was a moment of madness.”
The attack follows a rare nationwide police strike on Wednesday, which saw thousands of officers demonstrating in Paris over working hours, shortages in resources and controversial pension reforms.
Police unions say there have been more than 50 suicides by police officers since the start of the year.
They blame the rising numbers on difficult working conditions and increasing violence towards police.