Police say the situation is now under control, and neither law enforcement nor civilians were injured.
France is currently in a state of emergency after being hit by a wave of deadly terror attacks in recent years.
A policeman was shot dead and two others were wounded in an attack on the Champs Elysees in April, just days before the presidential election.
The national police Twitter account had earlier said (in French) that there was an "ongoing police operation", warning people to respect the security cordon.
French media, quoting police sources, say the act was deliberate.
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