Explosions and gunfire rang out early Wednesday as heavily armed police surrounded a suburban Paris apartment where suspects are holed up.

A police official said officers exchanged gunfire with the people inside, and several police were injured. The extent of their injuries was unknown.

It was unclear whether there were injuries among the suspects.

Two officials said the police operation was connected to the investigation into Friday's gun and bomb attacks that killed 129 people.

Police vans and fire trucks rushed to the scene in Saint-Denis, north of Paris. The site is less than two kilometers (just over a mile) from the Stade de France stadium, which was targeted by three suicide bombers during Friday's attacks.

Police cordoned off the area nearby, including a pedestrian zone lined with shops and 19th-century apartment buildings. Riot police cleared people from the streets, pointing guns at curious residents to move them off the roads.

Saint Denis Mayor Didier Paillard said public transport was suspended and that schools in the center of town would not open Wednesday.

A resident said an explosion shook the neighborhood at about 4 a.m. (0300GMT).

"Then there was second big explosion. Then two more explosions. There was an hour of gunfire," said Baptiste Marie, a 26-year-old independent journalist who lives in the neighborhood.

Another witness, Amin Guizani, said he heard the sound of grenades and automatic gunfire.

"They were shooting for an hour. Nonstop. There were grenades. It was going, stopping. Kalashnikovs. Starting again," Guizani said.

Seven attackers died in Friday's gun-and-bomb rampage through Paris that killed at least 129 people and left over 350 wounded. The Islamic State group has claimed responsibility for the carnage.

Police say they are hunting for two fugitives suspected of taking part as well as any accomplices.

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Associated Press writers Angela Charlton and Jill Lawless in Paris contributed.