Armed police have raided a flat in the north Paris suburb of Saint Denis in an operation linked to Friday's attacks.
Watch a live stream of police on site in Saint Denis:
A female suspect blew herself up with a suicide belt, a prosecutor says. Some reports suggest two suspects died. There were explosions and gunfire in the operation, which is continuing.
Five people have also been arrested.
The focus of the operation is reported to be Abdelhamid Abaaoud, the alleged mastermind of the Islamic State-claimed attacks that killed 129 people.
Roads have been blocked off around Rue de la Republique in Saint Denis, in the same district as the Stade de France, where suicide attackers detonated bombs on Friday.
Truckloads of soldiers joined armed police at the scene.
"I've been hearing gunshots continuously, like fireworks... There have been some breaks but .....to me it sounds like continuous gunshots," one resident, Benson Hoi, told the BBC.
At least five people were believed to have been in the targeted third floor flat in Rue de La Republique, French radio RTL reported.
At least two police officers had been wounded.
The operation began at 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."
Belgian Abdelhamid Abaaoud, 27, had been thought to have organised Friday's attacks from Syria, but is now believed to have been one of the five in the Saint-Denis apartment.
Earlier, security sources said surveillance video showed a possible ninth assailant during Friday's attacks.
The video 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 near simultaneous attacks on bars and restaurants, a concert hall and the Stade du France left more than 400 people wounded, with 221 still in hospital, 57 of them in intensive care.
European countries are 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 Hanover's 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.