Heavy shooting has been heard in the northern Paris suburb of Saint Denis and reports say a police operation linked to last Friday's attacks is under way there.
Some police have been wounded, French TV station BFMTV reported.
Earlier, security sources said surveillance video showed a possible ninth assailant during Friday's attacks in which 129 people died.
The so-called Islamic State (IS) group has said it carried out the attacks.
One report said roads had been blocked off around Place Jean Jaures in Saint Denis.
The Stade de France, where suicide attackers detonated bombs on Friday, is in the same district.
Amateur video aired by TV stations BFMTV and iTele cited witnesses saying sporadic gunfire had rung out since around 04:30 local time (03:30 GMT).
Deputy Mayor Stephane Peu urged local residents to stay indoors, saying "it is not a new attack but a police intervention".
Friday's attacks also left more than 400 people wounded, with 221 still in hospital, 57 of them in intensive care.
The video released earlier reportedly shows a third figure in the car carrying the group which attacked several bars and restaurants.
It is not clear if this ninth attacker is one of two suspected accomplices detained in Belgium or is someone still on the run.
The deadly attacks have put European countries on high alert. On Tuesday evening, a football friendly between Germany and the Netherlands was cancelled shortly before kick-off and the stadium in Hanover evacuated after "concrete" information about a bomb threat, according to the city's police chief.
Part of Hannover railway station was also closed while a suspicious object was investigated.
Meanwhile, two Air France planes heading to Paris from the US were diverted because of security threats. One was sent to Halifax in Canada, the other flew to Salt Lake City in the US state of Utah. Both planes landed safely and the passengers were unharmed.