French police shot dead a man who lunged at them early on Monday with a long-blade knife at Paris's Gare du Nord train station, police sources said.

The man attacked two police officers on patrol at the station, one of Europe's busiest, with a 30-centimetre (12-inch) knife with the English slogan ACAB (All Cops Are Bastards) written on the blade, said one police source, who asked not to be named.

"The police used their firearms, thus eliminating all danger, both for themselves and for travellers," Interior Minister Gerald Darmanin wrote in a tweet.

The attack occurred around 7:00 am (0600 GMT), he said.

The station is the hub for Eurostar trains to and from London and Thalys trains that link France with Belgium and the Netherlands, as well as high-speed trains to the French north.

A France Television journalist who was at the train station at the time posted a video of the incident on social media, in which two gunshots can be heard.

"It was an individual known to the police as someone who wandered around in the station," Transport Minister Jean-Baptiste Djebbari told RMC TV.

"He appears to have attacked the police with a knife, forcing them to use their weapon."

France is still on edge after hundreds were killed by militants in attacks in 2015 and a spate of isolated strikes at the end of 2020. Authorities have not however linked Monday's incident to terror.

National anti-Terror Prosecutors told AFP that they had not been asked to open an investigation.

Security is set to be a crucial theme in the April 2022 presidential election, where President Emmanuel Macron is expected to seek a new term. His main challengers are on the right and far-right.

Police representatives have for months been calling on the government to ensure better protection for police, who themselves have been under fire over allegations of racism.

Paris police chief Didier Lallement applauded the "courage of the police who reacted calmly to a cowardly attack".

Police union Alliance described the attacker as an "anti-police terrorist" who had targeted the police "with a knife in order to kill them".

"This shows again how the protectors of the Republic risk their lives in the street, outside a church or on a daily patrol in a station."