French police have begun a murder investigation after a civilian employee went on a terrifying stabbing rampage inside Paris police headquarters, killing four people before being shot dead inside the compound.

Officials declined to say what the motive was for the attack, which took place at lunchtime on Thursday local time.

Paris prosecutor Remy Heitz said authorities had opened a murder investigation, for the moment ruling out a terrorism inquiry.

Armed with a knife, the 45-year-old civilian technology administrator in the police intelligence unit, launched the attack in his office and then moved to other parts of the large 19th century located across the street from Notre Dame Cathedral.

He stabbed to death three police officers and an administrative worker before he was shot dead by an officer in the compound’s courtyard, French officials said.

A fifth person was critically injured and was undergoing surgery.

French interior minister Christophe Castaner said the employee had worked for the city’s police force since 2003 without ever arousing concerns.

“There were no warning signs,” Mr Castaner said.

“This man was known inside the computer department. He worked alongside his colleagues and never presented any behavioural difficulties.”

The shocking knife spree occurred in one of central Paris’ busiest tourism neighbourhoods near the Notre Dame Cathedral which is undergoing reconstruction after a massive fire partly destroyed the 12th century building in April.

Police and soldiers block off the Paris police prefecture after a knife attack. Photo: Getty

Mr Castaner described the man as a “model employee” who had worked there for 16 years.

Police union official Jean-Marc Bailleul said it was a “moment of madness” rather than a terror crime as reports emerged the employee had experienced issues with his managers.

It has also been reported the man converted to Islam about 18 months ago but police are yet to make any terrorism links.

Police official and lobby group “Police Up in Anger” member Christophe Crepin was quoted as saying the IT worker had issues with his supervisor, the ABC reported.

“I know there were tensions between him and his direct supervisor,” Mr Crepin said.

“I do not think this is a terrorist act,” he told Franceinfo Radio.

France 24’s Catherine Norris-Trent reported “chaotic” scenes inside the police building.

“Sources describe a chaotic, confused situation,” she posted on Twitter.

NEW: Paris knife attacker who killed 4 in police headquarters had recently converted to Islamhttps://t.co/Cc2WsvPt6k

— Ryan Saavedra (@RealSaavedra) October 3, 2019

The area around the police headquarters was sealed off and a metro station was shut for security reasons as the attack unfolded.

Police have been searching the attacker’s home and his wife has reportedly been brought into custody as anti-terrorist investigators evaluate what happened.

Paris State Prosecutor Remy Heit (L), French Interior Minister Christophe Castaner (C) and Paris Police Prefect Didier Lallement outside the Paris Prefecture on October 3. Photo: AAP

Speaking outside the police headquarters, Mr Castaner said the attacker was known to his colleagues and had worked for some time in the IT department.

“He had never presented any behavioural issues, he had never presented the slightest cause for alarm before going on his deadly rampage today,” Mr Castaner said.

President Emmanuel Macron, Prime Minister Edouard Philippe and Interior Minister Christophe Castaner have all visited the site.

For the first time in 20 years, the National Police unions called for a ‘March of Wrath’ after 50 police have killed themselves since the beginning of the year. Photo: AAP

The attack came in the same week thousands of police marched through the streets of Paris, protesting at poor working conditions they say have led to dozens of suicides among their ranks this year.

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.

-with AAP