A knife-wielding employee killed four of his co-workers at police headquarters in the centre of Paris before being shot dead by police.

Key points: It is believed the attack began in the police building and then continued in a compound across the street from the Notre Dame Cathedral

It is believed the attack began in the police building and then continued in a compound across the street from the Notre Dame Cathedral The attacker worked in the police building and had not posed problems before

The attacker worked in the police building and had not posed problems before The area surrounding the police station was put in lockdown

The man has been identified as a 45-year-old IT assistant.

Officials are yet to confirm the motive of the attack and say they are not treating it as terrorism at this stage.

Three men and a woman were killed, according to Paris prosecutor Remy Heitz. Another person was wounded and is undergoing surgery.

Mr Heitz said police were searching the attacker's home. His wife had been brought into police custody but not charged, the Paris prosecutor's office said.

French emergency crews outside the Paris Police headquarters. ( REUTERS: Christian Hartmann )

'Moment of madness'

Speaking outside the 19th century police headquarters near Notre Dame cathedral, French Interior Minister Christophe Castaner said the attacker had worked in the IT department of the city's police force since 2003.

"There were no warning signs," Mr Castaner said.

"He had never presented any behavioural issues, he had never presented the slightest cause for alarm before going on his deadly rampage today."

A police official and member of the collective "Police Up In Anger", which lobbies for better conditions for officers, was quoted by franceinfo radio as saying the assailant had experienced issues with his supervisor.

"I know there were tensions between him and his direct supervisor," Christophe Crepin said. "I do not think this is a terrorist act."

Jean-Marc Bailleul, a police union leader, described the incident as criminal rather than an act of terror.

"It was a moment of madness," Mr Bailleul told BFM TV.

Some French media outlets reported that the attacker had converted to Islam 18 months ago.

Police union official Loic Travers earlier told reporters the attack appeared to have begun in an office and continued elsewhere in the large police compound across the street from Notre Dame.

He said he could not remember an attack of this magnitude against officers.

Four officers were fatally stabbed inside the Paris Police headquarters. ( Reuters: Philippe Wojazer )

Emery Siamandi, an employee at police headquarters, said he heard gunshots and immediately saw two officers come outside an office weeping.

A third officer, who Mr Siamandi described as the person who shot and killed the assailant, was on his knees, also in tears.

"I tried to see if it was a terrorist attack or maybe several people had walked in to kill people," he told journalists after he was evacuated.

"I was suspicious and very soon I saw policemen with their guns drawn — they had guns.

"Where I was, 99 per cent of people were policemen."

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.

The area surrounding the police headquarters was put into lockdown. ( AP: Kamil Zihnioglu )

The neighbourhood, one of Paris' busiest tourist attractions, was locked down, the Cite metro stop was closed and a nearby bridge was blocked off.

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./

AP/Reuters