Video report by ITV News Correspondent Paul Davies
A police employee armed with a knife has killed four colleagues in a "deadly rampage" at the Paris force headquarters, a French police union official said.
Three of the victims were men and one was a woman - and three were police officers, with one an administrator.
The 45-year-old killer, an IT worker in the police intelligence unit, launched the attack in his office then moved to other parts of the large 19th century building across the street from Notre Dame Cathedral.
Police union official Loic Travers said the killer had worked for the force for about 20 years, was employed in the intelligence unit and had not posed known problems until Thursday.
An officer stopped the attack when he shot the assailant in the compound's courtyard.
Christophe Castaner, French Interior Minister, described the incident as a "deadly rampage".
"This man was known inside the computer department, he worked alongside his colleagues and never presented any behavioural difficulties, never any warning signs," he said.
"And this morning he went on deadly rampage."
Emery Siamandi, an employee at police headquarters, said he heard gunshots and immediately saw two officers come outside an office weeping.
"I told myself, this isn't right," Siamandi said. "Moments later, I saw three policewomen crying. I couldn't help them in any way, and their colleagues were crying, too, so I figured it must be serious."
A third officer, who Siamandi described as the person who shot and killed the assailant, came out on his knees, also in tears.
French media reported that a staff member carried out the attack with a ceramic knife in part of the prefecture that is not open to the public.
"It's the worst scenario possible, an internal attack with colleagues working together," said Philippe Capon of the UNSA police union.
Capon cautioned against jumping to conclusions on the motive and said: "Nothing can be ruled out, including a personal issue."
The neighbourhood, one of Paris' busiest tourist attractions, was locked down, the Cite metro stop was closed and the bridge between Notre Dame and the headquarters building was blocked off.
French President Emmanuel Macron is travelling to the police headquarters. His office said the president wanted to show solidarity and support toward all police officers and employees.
The attack came a day after thousands of officers marched in Paris to protest against low wages, long hours and increasing suicides in their ranks.
Extremists have repeatedly targeted French police in France in recent years.
In 2017, a gunman opened fire on the Champs-Elysees boulevard, killing one officer before he was shot to death.
In 2016, an attack inspired by the Islamic State group killed a police officer and his companion, an administrator, at their home in front of their child.