Four people have been killed in the stabbing at the Paris police headquarters, according to CNN affiliate BFM TV.

Loïc Travers, a police union secretary, told BFM TV that five were dead, including the attacker.

The motive of the attacker, who was a longtime administrative employee for the police, is still unknown.

“He has been with us for over 20 years,” Travers said, speaking outside the police headquarters.

The Cité metro station in Paris was closed Thursday afternoon as a security measure, the French metro body said on Twitter.

The station is on the Île de la Cité, where the police headquarters and Notre Dame cathedral are situated.

A police officer outside of the perimeter told CNN: “Île de la Cité is now a real island, no one can go and leave.”

This is a developing story, follow the update on CNN.com.